absorption Image


Victron Inverter chargers and float voltages ? why do they not retain ...

Good day all . A question thats been burning me for a while .. given that ive installed alot of lead acid and lithium systems i have been evaluating the charge and float profiles and their results ... i find this alot in systems with Standby application no solar .. and alot with No comms to batteries no canbus or DVCC enabled.. Just a plain backup ..
So Scenarios are such inverter charging battery from the grid and battery permanently connected to the inverter as should be.
the inverter charges up to 100% and reaches 55.7v (16s Lifepo4)
then the system switches to float where is should retain voltage --- NOT HAPPENING
then a rebulk or re absorb should take place in 7 days .. ---NOT HAPPENING

technically a 0.2v per 12v method is used meaning in a 48v system we should get a drop on float voltage of 0.8v to get a reabsorb ... ---- NOT HAPPENING.

Alot of battery systems use contactors and Bms systems internally which account for internal draw from the battery cells . and in which case means that the battery does take some load to retain the voltage from the inverter ..
We get to point where the SOC falls and falls and battery is never recharged with lithium ticked ...

But why would this not take place on the inverter with a predefined float value is my question and why does the deviation value not kick in the recharge .. when lower then 0.8v below float ?

A little more details i feel should be added in .
Two different inverter units, one multiplus 3000va 48v unit
the other multiplus 5000va 48v unit.
Both when set to a float voltage of 50.6 to 50.7 charge the battery to 100% Lifepo4 . 15s configuration .. after this process they dont retain the float voltage of 50.7 ... the battery has bms and circuitry internally that uses power.
Storage Not ticked .
Lithium batteries Ticked on
Both units are used only for power back up purposes and both units have Venus GX connected .. Pulling my hair out .
Please can some one chime in .. I dont want to have to run with DVCC as this is not 100% working and surely the default profile to Float maintain voltage should do its job unless i am missing something often after two weeks or so the voltage of the batteries drops to around 48v .. Not good .

Nismoboy34 asked
Nismoboy34 edited ·

0 Answers

How would i know if my battery charge.

I have a Multiplus II. How would i find out if my battery charge. What is the difference between float & absorbtion.

Dina asked
Justin Cook - Bay Marine Supply USA answered ·

1 Answer

re-bulking and absorption questions

Good day all, i have a couple of questions i hope someone can enlighten me on, i have 4 smartsolar 100/20's on a VE network charging a 600ah vrla battery, bmv-712 also on the network, currently the chargers all have the same settings, float voltage is set at 55.2v, Re bulking should commence at 54.8v after 1 minute, this does not happen, currently the battery is at 54.1v and dropping, charge power is 500w in float at this point, any reason why the controllers won't re bulk? the units never achieve absorption voltage (58.6v) they always cut to float at 57.8v by mid to late morning (lowest morning voltage is 48.75v but is going down every day, lower highs and lower lows). Absorption mode is set to adaptive. Has anyone had similar issues? all firmware is up to date. Cheers, Maxx.

Maxxpwr asked
Maxxpwr answered ·

2 Answers

Syncing MPPT Ve.direct & 150/70 Ve.Can


I still have an issue with a new 250/85 going to float to early. It is in a parallel with a 2 x 150/70s connected with VE.Can. Will I be able to sync these with a GX device ( or Pi running Venus)using the VE.can ports and VE.direct ? They all Bulk charge together, but the Absorb time on the 250 is not long . The batteries are charging nicely however.

JDM asked

0 Answers

Nach Update auf V1.50; Warum lädt der MPPT 75/15 Laderegler nur noch in Erhaltungsspannung (Bulk) ?

Hallo, wir haben einen Smart Solar MPPT 75/15 an einem 110 Watt Solar Panel und einer 225 Amp/h Batterie installiert.

Vor dem Software Update auf V.1.50 hat das System toll funktioniert.

Bulk und Float alles ok. Siehe bitte Foto.

Nach dem Update auf V1.50 kennt das System nur noch Bulk - Ladung.

In den Tagen vor und nach dem Software Update waren keine Stromverbraucher aktiv. Auch sonst wurde nichts am System verändert.

Wir haben nun seit 3 Tagen Verbraucher hinzugeschaltet. Das System lädt weiterhin nur in Erhaltungsladung - Bulk weiter. Die Sonneneinstrahlung ist in den Tagen vergleichbar.

Warum lädt der MPPT 75/15 nur noch in Erhaltungsspannung (Bulk) ?

Gibt es ein neues Softwareupdate? Oder kann man auf die alte Software Version zurück wechseln?

Vielen Dank schon einmal im voraus für die Informationen.


Wesso asked
Stefanie commented ·

2 Answers

Multiplus-II Absorption and Float - discharging to grid


I have an ESS installation with a Multiplus-II 5000/48, an MPPT 150/85 with 4Kw solar system and a 48V 200Ah LifePo4 battery system (currently no BMS). Absoprtion voltages are 56.4 on the Multi and 56.8 on the MPPT - float at 54.4. There is some behaviour that is concerning me in that during absoprtion and float, the Multi seems to be continuously switching between charging and inverting, this happens during the day where the data logs look more complex due to varying AC loads and MPPT but it also happens during scheduled charging overnight, see plot below. You can see the half-hour absoprtion phase from around 00:20 to 00:50 where amps oscillate between +5A and -10A, then folllowed by a large amp spike (selling to the grid) at 00:50 when it switches to float (I believe this is caused by the drop in voltage - hence the battery needs to discharge current to achieve that. In float mode (from 00:50), the same behaviour continues, going from charging to the discharging.

I feel this is neither good for the batteries nor for the Multiplus - am I doing something wrong or areany of my settings wrong? I am running Mode 1 ESS self optimised.




tkrull75 asked

0 Answers

Absorption end amps for Victron 110Ah AGM deep Cycle Batteries

Hi I Have 5 x 110Ah Victron AGMs in parallel for 550Ah bank , Can anyone advise the end amps in absorption for these ? have heard everything from 1-4 % from watching them a little when on generator through Phoenix charger and inverter it switches to float around 10-11 amps so about 2% does this seem right , alot of people say AGM's should be set higher than this at 3-4 %

Simon Phillips asked

0 Answers

End of absorption with tail current

Hello. I wonder if I am thinking this right... I am trying to end the absorption phase solely based on the tail current, but it seems system is ignoring that.

Scenario is: Charging LiFEPO4 bank with 8 cells (25.6V) with integrated BMS just for protection (no communication with Victron)

- Multiplus 24/ 3000

- 3x MPPT in parallel charging

- Venus GX

Customised charge profile:

- Absorption voltage: 27.6 V (I can monitor cells, and no cell is above 3.6V)

- Absorption time: Fixed, 1hour 30 minutes

- Tail current: 9 amps, battery capacity is ~180Ah

- Float voltage: 27.1 V

It ignored the tail current and the absorption time was exactly 1,5 hours. I would like to stop absorption when current decreases past 9A.

I didn't feel adaptive time was ok for lifepo4, as if bulk takes longer, absorption may not need so much time. I would like to make the criteria to stop Abs be solely the Tail Current (system!, not individually each MPPT)

How can I do this?

Elimac asked
Elimac commented ·

2 Answers

Voltage Spikes, System Failure, MultiPlus Absorption Transition During Charging LiFePO4

System Design:

I have 3 Lion Energy UT1300 LiFePO4 105Ah batteries. They each have an internal BMS and are the 'drop in' replacements for deep cycle Lead Acid batteries. They are rated for maximum 100A charge / 150A discharge each and are connected in parallel using 4/0 AWG cables. On the negative terminal I have 12" 4 AWG cable to a BMV 500A shunt and then 24" 4 AWG cable to a Lynx Shunt. On the positive side I have 24" 4 AWG between the battery bank and a BlueSea m6000 disconnect switch, then 12" 4 AWG from the switch to the Lynx Shunt. The Lynx Shunt is connected to a Lynx Distributor. Then I have a MultiPlus 12/3000/120 connected to the Lynx Distributor via (2) 36" 4 AWG cables and a 400A Mega Fuse. The Lynx Shunt has a 800A CNN fuse. The MultiPlus has the voltage sense connected using a fused 20 AWG wire to the battery terminals. I know the 4 AWG wiring is not ideal, I will replace with larger wire in my final installation, I don't know if it is the source of my issue. Here is a crude wiring diagram



I can discharge the batteries fine, the problem occurs during charging. When the MultiPlus transitions from Bulk to Absorption problems occur. They range from interrupted charging (Absorption voltage set to 13.9 - 14.1) to complete shutdown of the MultiPlus (Absorption voltage set to 14.4 - 14.6).

Here is a picture of the PV during charging showing the transition between bulk and absorption. The absorption voltage is set to 13.9, the unit seems to stop charging after the transition to absorption.


Here is the picture of PV when the MultiPlus absorption voltage is set to 14.4 Volts. The drops during the absorption mode represent when the MultiPlus shuts down and then resets itself. During the shutdown all lights are off and AC1 is off. NOTE: The voltage spikes seem to follow the current peaks. The MultiPlus will continue this interrupt cycle indefinitely until I intervene.



1. Has anyone else seen this behavior?

2. Could this be caused by the BMS shutting down during charging?

3. Could this be caused by using 4 AWG cable?

4. Could the MultiPlus design be causing the voltage spike?

5. What would a normal PV chart look like during absorption mode? I have read absorption mode is a constant voltage with reducing current until charging is complete.

Thanks in advance for any help.

mtnscott asked
Daniël Boekel (Victron Energy Staff) commented ·

4 Answers

250/85 going to float 150/70 x 2 still in absorb

I just expanded an existing installation by adding a 250/85 to an existing system with 2 x 150/70 charge controllers . All wired up this afternoon, but the new charge controller is just sitting in float rather than charging as well. The old chargers are in absorb and the new addition goes straight to float, meaning the new array is not doing anything . Is there a fix for this ? One thought I had is the the 150/70s are using the adaptive charging ( which I cant change) and the new one I have set to fixed absorb time . The 250/85 didn't even run through its full absorb time before going to float

thanks in advance

JDM asked
JDM edited ·

2 Answers

SOC setting for absorption

If SOC % is usually not correct then why can't the setting for when bulk finishes be a voltage setting instead of a percentage setting? Is that possible victron?

Daren Connor asked
Daren Connor commented ·

2 Answers

SOC in VE Bus is not matching the battery

I have 3 x 48/5000/70 multiplus in a 3 phase configuration which is fed by a 15kw Fronius 3 phase solar inverter.

Lately the SOC in VE Bus does not match the batteries. This causes the SOC to stop st 90% SOC when the batteries are at 57.6v which is the absorption voltage. Sometimes it will sit at 90% for 3 or more hours waiting for the batteries to meet the SOC before going into absorption. I've tried everything I can think of but I'm obviously missing something. Even my installer is at a loss. Can someone please help. Thanks in advance...

Daren Connor asked
Daren Connor commented ·

1 Answer

MPPT 250/100 Absorption timer with NIFE

The Absorption timer for Lead Acid battery types is set at the beginning of every day. However this doesn't work well for NI-FE (nickel iron) as the voltage will rise once a load is disconnected. The batteries can be 100% depleted (down to 9.5V), the load will then disconnect and the voltage will rise to as much as 13V. If the Absorption timer was to be set at that point in time any charge controller will act as if the batteries are basically fully charged.

What I need is for the charge controller to keep track of the lowest observed voltage over the entire discharge cycle then use that value to set the Absorption timer. I'm guessing nothing like this exists right now, but that would be nice thing to have in the future.

For now however, can I do this via a raspberry pi through either ve.bus or ve.direct? If i were to manually set the Absorption timer Automatically myself, I assume I can use something like Linux VictronConnect to issue commands every morning from my raspberry pi?

A complication is I need 2 MPPT charge controllers in parallel so I would need to issue the commands to both controllers around the same time, and I would assume via ve.bus? Or would I have 2 ve.direct devices?

Obviously there are a lot of moving parts here, and I have a lot more research to do, but is what I'm proposing here even possible or can anyone here offer reasons why this is not such a good idea. :)

Thanks in advance.

bbobkins asked
bbobkins commented ·

2 Answers

Disable "Repeated Absorbtion" for a Multiplus

How do I disable the "Repeated Absorbtion" for a MultiPlus Compact?

It's a Stand-by UPS application with a drop-in 12.8V Lithium battery with built-in BMS.

Floating at 13.4V keeps batteries fully charged. I'm thinking I should take them even lower than that, to prolong battery life.

No need to repeat Absorbtion, it's just pointless stressing the batteries, even at 45 days.

MondeoMan asked
TTbb edited ·

2 Answers

Are these reasonable readings for a Multiplus SOC shutdown?

I went out of town for several days and after three unplanned cloudy days, the system shut down as expected. What wasn’t expected was the readings when I got home and turned on the generator to charge the batteries. The first image below shows what the status was when I first turned it on. As you can see, the SOC is 41% after about 15 minutes of turning the generator on.


I was wondering why it was floating if the batteries were at 41%. After 90 minutes of no change, I started looking into why the Multiplus was floating instead of bulk charging. I found a couple of messages in the Community that suggested switching it to “Charge only” as a way to reset the Multiplus. So I did and it switched to absorption mode (at 9:11pm).

Immediately after doing that, the next reading I got was 85% SOC. Literally five minutes later, I got the following: 100% charge and back to Float at 9:59pm, for a total elapsed time of 48 minutes.


So my questions are:

  1. Is it to be expected that a system that was shutdown due to SOC settings should go from 41% to 100% in 48 minutes?
  2. Was it some kind of hiccup in the system that I needed to change it to Charger Only for it to go off Float to Bulk and then Absorption charge?
  3. If this is abnormal, what do I need to do to get a better understand and control of this behavior?
  4. Are there settings I need to change?

The battery bank is eight 6v 385ah batteries in series/parallel at 24v.



Todd Landfried asked
kai commented ·

1 Answer

Absorbtion Issues, BlueSolar Charger MPPT 150/85 (VE.Can)

I have my absorb setpoint Voltage at 55.36v and my absorb time is 20min. (Lithium batterys)

Today is an example of what can happen often with this charger. At 10:15AM with a burst of sun and strong PV output. The battery's reached 55.36v setpoint to trigger absorb.

Then shortly After this A cloud passed over reducing PV output (or some days it could be a large load in the home activates) this reduced the battery voltage to well below the Absorb Voltage setpoint.

This struggle up and down continues over the 20min absorption timer dropping back to Float at 10:35am.

My past experience with other charge controllers is absorb shows up as a Constant voltage stage and a dead flat line on the graph if the PV output is available to do so. If for some reason they can not maintain the voltage setpoint and the voltage reduces. Then the absorb timer stops counting down and restarts when in can. This insures you actually do get the programmed time at the constant voltage setpoint.

As you can see I'm lucky to have spent 30 seconds in total over the 20min absorb actually at the 55.36v setpoint.


OffgridSA asked
OffgridSA commented ·

2 Answers

PV rapidly fluctuates between 1 and 130w in Bulk - Battery voltage spikes to 14.65 then drops.

Hi, I'm getting some worrying behavior from my set up today. Not something I've seen before. It's a mixed day with clouds and then full sun.

When overcast everything seems normal.

When the sun comes out the PV wattage jumps right up and the battery voltage spikes to about 14.65 volts. Then the wattage then immediately cuts right back to 1 and the battery voltage reduces to 13.3ish. The watts and voltage then jump up and rapidly max out again, and the cycle repeats.

It is doing this in both absorption and bulk mode. The absorption voltage is set to 14.4v and float is set to 13.67v.

My equipment is:

  • 100/20 MTTP
  • MTTP Control
  • 200w 24v Victron Panel
  • 100Ah 12v pure lead/carbon battery
  • BMV 700

Having done this all morning - rapidly fluctuate between 1w to 130w PV and 13.3v to 14.65v battery in both absorption and bulk modes - it's now stable in float at 35w and 13.64v.

Is this normal?

Atomix asked
Atomix answered ·

2 Answers

high battery voltage Victron Multiplus

We experienced High Battery Voltage Alarms on 2 Multiplus 48/5000/70 systems.


- mode "Keep batteries Charged'

- both in Absorption mode

- Absorption voltage set to 55.2

However, with both systems the battery voltage went up as far as 58 V, triggering Alarms which cleared after about 3 hours, when voltage went back dropped back to around 55V.

What could be the cause of this?

peter van duijn asked
MaSi commented ·

8 Answers

Issues with BULK CHARGE not staying on. MultiPlus 12/2500/120 with Multi Control

Not so new but still good Trojan deep cycle 6 volt large battery bank (12 units),
Charging system:
Solar panels, micro hydro electric,
New Genset Honda 2200W Inverter connected to battery charger.

I can't get the charger to stay on "Bulk charge" like it should. The built in charger kicks off quickly to taper down to float charge way before the battery bank is not even close to be charged. It usually kicks off Bulk charge in about 5 minutes.

  • I keep the multi control setting at 18. (Could it be higher with 2200W genset???)
  • Solar panels/micro hydro seem to charge the battery bank no problem...

Possible causes of charger Bulk charge issues?

  1. My guess is the battery bank is getting old and I need to readjust the settings (INFO PLEASE...)
  2. Wrong charger settings? (INFO PLEASE)
  3. Bad connection? (checked everything)
  4. Faulty temperature sensor? (Checked connection) (Should I disconnect it for test?)

I disconnected the solar panel system and getting the same problem...

Thank you Victron. These units are amazingly durable and well built. This community page is well put together AND HELPFUL (I hope!). I will definitely get a new unit if this one ever gives up...

Patrick, Canada

Blackbox asked
Blackbox commented ·

1 Answer

Solar MPPT 150/45-TR suitable for tesla packs ?

Hi @all !!

it the above mentioned mppt charger able to charge a tesla pack in 12s Configuration ? Absorption should start at 49.2 Volts, Float 49.1 Volts.

I would like to add 90 Volts of Solar input voltage. Is that enough for the charger to work probably ?

Thanks a lot !


stxShadow asked
WKirby answered ·

1 Answer

Victron MultiPlus-II 48/5000/70-48 keeps shutting down on changeover from bulk charging to absorption mode, help?


I have a Multiplus 2 connected to a Victron battery (70Ah). The system shuts down after bulk charging as soon as it is about to go into absorption.

Please help

Daniël Boekel (Victron Energy Staff) commented ·

2 Answers

Why is my Quattro sending 30.07 volts to my 24 v batteries???

I have a Quattro 24/5000/120 connected to a pair of 12V lithium batteries in series, with a BMV 712 monitoring them.

I usually don’t allow a full absorption cycle to run, but the last few days I’ve let it complete the cycle to resync everything. And I’ve actually left the system to manage the batteries as “normal” allowing it to keep them full. It’s been “short cycling” the recharge as the batteries are mostly full, but discharge slightly over float then restarts the bulk cycle.

Since then, I’ve noticed my battery BMS throwing a high voltage alarm and I traced it down to my Quattro sending over 30 volts to my batteries!!

How can this happen?

My absorption voltage is set to 28.4 and float is 27.2.

This appears to happen just as it’s switching from bulk to absorption. It happens pretty fast and sometimes VRM doesn’t even catch it. This time it did.

Is this normal?

This is quite concerning since that voltage is way too high for these batteries.



Geomz asked
ben commented ·

1 Answer

When is Victron going to fix the crippling bugs in their MPPT controllers?

Six months ago, following multiple user complaints, I posted this, outlining how Victron MPPT controllers consistently fail to fully charge batteries in intermittent sun, due to a bug in their "smart" Absorption timer algorithm.

"Fast" forward to last week, and finally a supposed solution is given in terms of an update to Firmware 1.42.

Except it's not.



Nothing has changed with v1.42 at all. The controller is still resetting to its shortest absorption period every time a cloud goes over, and dropping to float when the batteries are desperate for charge. And yes - I manually ensured the battery V was under 12V every sunrise, and I did isolate all loads during the day for these tests - that difference in Amps between the app and the Trimetric is just Victron's apparently poor accuracy (another problem in its own right).

This isn't some obscure, niche problem. This is core function - reliably controlling the absorption stage length is the fundamental point of a controller. It's been reported again, and again, and again, and again, and again, and again. We have a suspected case where it's ruined someone's batteries as a result. For it to take six months for this to be addressed, while adding pointless gimmick charts to the app instead, was poor enough. For it to now turn out to be a non-solution is unacceptable.

I'm addressing this squarely at you @mvader (Victron Energy Staff). You promised this was being fixed when I first bought it up. Your response here determines whether I take this unit back for a refund.

StraightUp asked
mvader (Victron Energy) commented ·

4 Answers

why can i not set absorption time in blue solar charge controller 100/50

i have set charge voltage and float voltage to rolls recommended voltages but i can not set the absorption time. i am in user defined setting. it should be 4.2 hrs and it is stuck on 6hrs.

any ideas please

Robin asked
Mark answered ·

3 Answers

Field Test: Why Victron MPPT controllers use incorrect absorption times.

So, after this topic coming up in multiple different threads recently, @Leslieanne proposed a theory as to why so many users are finding their Smart/Blue Solar units are only doing ~1hr absorptions, despite having quite a low battery voltage at sun up.

In short, the theory is that if you have significant enough shading on your panels at some point during the bulk stage, the panel voltage drops below cutoff, as if encountering 'sundown'. When the shading is removed, it goes through another 'sunrise' and recalculates the absorption time, using the below table...but with a new, much higher battery voltage - resulting in drastically shortened absorb phases.


Considering I personally run float=absorb, I've never actually looked at my 'absorb' times. So I decided to test this. For the last 5 days, I've run my batteries (370Ah) down to 30% each night to guarantee consistently low startup voltage, then isolated any loads all the way until the next sundown (ie no power draw while charging). Whilst it's meant a week of cold meals (which have not impressed the wife) this has guaranteed a consistent test environment, in which the controller SHOULD provide the full max absorb time - set at 6 hrs.

And it did! Well, at first:



Left to right, Days 1 to 3 were slightly cloudy but steadily clearing, hence the increasing yield. Day 3 in particular was solid sun and I was able to get a full 110% overcharge and even a brief equalization, completely restoring 100% charge. Importantly, each day correctly ran the max absorb time. The fun begins on day 4.

Being a sunny day, I had to resort to 'simulated' cloud i.e driving under a roof. Once the battery V reached 13v, I did one short tunnel pass and noted that sure enough, the controller drops out of charge and the blue 'bulk' light flashes, just like after sundown. It only takes a few seconds of sun loss, and sure enough....


As shown, the controller reset and recalculated a 1 hr absorb, based on a 'startup' voltage of 13.0v. Two further things to note here

Firstly, the total yield in this case has remained more or less the same , due to my float v = absorb v. Had this not been the case, by the end of the week I would have certainly totally killed the batteries.

Secondly this was with 70V panels on 12V batteries. With more typical 12/24V, I suspect you could trigger this with even cloud or treeshade.

As it happens, I tested this on the last day anyway. A storm front blew over and we had a good 5 minutes of twilight under some good Cb. Quick check to the meter and yep - the Victron dropped out at 12.4v, panel V fluctuating around 15-20v. Lo and behold, the result - a 1/3 absorb.


So, the conclusion?

These MPPT units are undeniably vulnerable to spurious absorption calculation, but @Solvan s theory that its due to inaccuracy in the units measurements is incorrect; they are accurate enough for their purpose, the problem is their own calculation algorithm.

Regardless of panel voltage, even a few seconds of major solar interruption by common events (driving through shade, sail blocking, dark clouds) will entirely disrupt this algorithm. This would be especially exacerbated if you were running a load at time of solar interruption, dragging V down further and likely cutting the most critical phase of charge by 80%. If you're not actively watching your SoC, or at least your end amps during float, this could easily result in chronic cumulative undercharging.

Victron needs to sort this out - this has the potential to damage customers' batteries. Its a very simple matter of extending the time required for low panel voltage to trigger a controller shutdown, from a few seconds to maybe an hour or so.

( Or, yknow - having a manual absorption configuration like every other controller on the market...)

@mvader (Victron Energy Staff)
@Guy Stewart (Victron Energy Staff)

StraightUp asked
StraightUp commented ·

3 Answers

BlueSolar MPPT leaves Absorbtion too early

MPPT leaves absorbtion with 30 Amps. Acctually, there are 2 MPPTs, each at apeox 30 Amps which means at 60 amps still absorbing. BMV does't synch, because max SOC keeps around 85% end there's plenty of sunshine.

Why that happens?

Battery bank is 1000 Ah at 48V, lead GEL chemistry.

MPPTs are 2x BlueSolar Charger MPPT 150/60 in parallel.

There are 3 x MultiPlus 48-5000 in patallel.

BMV is BMV-600S.




BSKZ asked
Xathros answered ·

2 Answers

How to determine absorption/float/equalisation voltage

Hi guys

I recently bought myself a BlueSolar MPPT 150/35 CC to use in combination with a battery bank, consisting of 2x 6 V gel lead acid batteries (for golf carts): Golf Cart TAB Motion Gel Batteries (https://www.tab.si/index.php/industrial/display_smalltraction/4 ).

Now I ask myself the question how to determine the right determine absorption/float/equalisation voltage for this type of batteries. This link (https://chargetek.com/basic-information.html ) gives like a general rule of thumb for lead acid batteries: 2.25/2.4/2.55 V/cell ==> 13.5/14.4/15.3 V

I found there's a pre-installed program for forklift batteries: PzS tubular traction (1), 13.8/14.9/16.7 V. As forklift batteries are more or less similar to golf cart batteries and these numbers more or less look like the ones I found above, I intended to use this mode. However, I'm not quite sure if the batteries are tubular, and if that even matters.

Is there any other (experimental) way to determine these voltages?

Also, I read that it is not advisable to equalise gel batteries, is this right? Why not?

Thanks in advance!

mielke asked
JohnC commented ·

1 Answer

Boondocking with BMV-712: SOC error? Best practices?

I have the following setup: smaller 2015 Lance travel trailer with 2ea 12V lead acid flooded batteries in parallel, BMV-712 and the standard Honda 2kW generator. The trailer's battery charger seems modern (3-stage charging, lots of amps, etc.).

I plan to boon dock (no shore power) regularly and would like to tune the BMV-712 to help keep the batteries charged, healthy, and to know when and how long I should run the generator.

From research, I know I should always keep the batteries above 50% capacity to avoid premature replacement costs. Also, without many hours of charging (e.g., plugged in or on solar), I cannot expect battery capacity to rise above 90% while boon docking.

When charging from, for example, ~60%, the charger will be in the "bulk" mode with high current, and rising voltage. This charge mode is the quickest, but only gets to 80% capacity.

Then the charge mode changes to "absorption" where the charger voltage is held high (14.6v in my case) and then the amps fall off toward ~2amps (in my case) when the charge mode changes to "float" at which the battery capacity is at 90%. To charge from 90% to 100% capacity would take many hours and isn't reasonable while boon docking.

Therefore, while boon docking, I should expect to cycle the battery between 50% and 90% depending on loads and generator run-times.

However, AFAIK, the BMV-712 is designed to treat the 90% charge state as "100% SOC" (?) The BMV-712 decides that when the voltage is the high "absorption" mode, and then the current drops below a "tail current", it proclaims SOC = 100%. But in reality, the battery is at 90% capacity at that moment (i.e., at the end of the "absorption" mode).

If starting from a full-charge (i.e., batteries have been plugged in for a day), the SOC value will be fairly accurate. However, if not starting from a true full-charge (allowing the BMV-712 to auto-sync the 100% SOC value at the end of the absorption mode), the reported SOC value will be 10% lower than reality. So the accuracy of the reported SOC value depends on whether the previous charge completed the float mode? Is this true?

If that's true, then I must tweak other settings to make the SOC value match reality or add-in some fudge-factor or work-around.

I could:

  • tell the BMV-712 that the "battery capacity" is 10% lower than the battery specification.
  • set my "SOC relay (charge floor)" to 60% instead of 50%, and mentally never let the reported SOC value fall below 60%

Is this a known problem with the BMV-712 SOC value? What do others do to work-around this inaccuracy?

Do other boon dockers have tips on using the BMV-712 to stay confident that the generator is running for the right amount of time?


goodguy5000hd asked
ben answered ·

1 Answer

BMV manual info unconformity (!?)

I was reading paper version manual for my BMV today, just to review my setting and try to learn more about it. But I got confuse cause I think there is contradicting information within. I had to go check the online version, to check if it was a typo that was maybe corrected. But I find the same error (!?) in the online version of the manual.

I'm saying this, but I might be wrong and confuse, please correct me if I'm wrong. I would really like to know which info is right or if the 2 info I think are contradicting are just 2 different info that I think should be the same..

so at 2.3 commons problems it is mentioned:


and when reading further, at 4.2.1 Battery settings under 02. Charged Voltage we found that:


and then if you just the mentioned section 3.7 (in blue ^) the mentioned voltage (13.2v) is proper for float and not for absorb, so think section 2.3 is wrong, unless I am just really confused and those 2 pieces of information are not related to each other...

so to add to my confusion, when I look at my own setup in the BMV, charged voltage is set to 14,8V, which I don't remember having set that, but I would really like to know if this is right or not

If ever i am proven to be wrong, i would like excuse myself in advance since english is not my first language

Simonmtl asked
Simonmtl commented ·

1 Answer

quattro charger absorption End amps


i've read something online


End Amps

End Amps is a trigger used by the charge controller to determine that the battery bank is fully charged and no longer accepting current. It is important to properly program the End Amps setting at the time of install. If this is programmed incorrectly or incompatible with the battery type sulfation will develop quickly.

As a battery reaches full state of charge its charge acceptance drops considerably. Typically, when the charge current falls below 2-4% of the battery capacity for 60 minutes the battery bank is no longer accepting charge and the Absorption phase should be terminated. Flooded batteries have a higher internal resistance, so we recommend setting End Amps at 2%. VRLA batteries, such as AGM & GEL, have a lower internal resistance. For these models it is recommended that End Amps be programmed closer to 3-4%.


where in the quattro can i setup the end amps to go from absorption to float mode?

Or how much is programmed in the quattro?

i see that on the shunt, but for what i know the quattro doesnt use that value and that value is just to auto sync the 100%


Kristof G. asked
Kristof G. answered ·

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