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AGM Battery

Battery voltage dropping with no load

Hello all,

Would be grateful for any help.

Off grid system for my tiny house. I have 2x 380W solar panels in series, 60A Victron MPPT charge controller, and 2x 140ah Sterling AGM deep cycle batteries in parallel.

Its been horrible and misty for weeks now. I moved out a couple of days ago because the charge controller hadn't gotten past Bulk charge for about 5 days. Today I went back at about noon to disconnect the fusebox incase there was any slight power draw. Victron app at this point reported a bulk charge and a battery voltage of about 13.8. I went back just now about about 4 hrs later and now the app reports battery voltage of about 12.8V. Having never left Bulk charge.

Why has the battery voltage dropped when there has been no power draw? It has been a horrible rainy day but I thought it would still manage to put something in the batteries?

Second question. I would like to know how to tell the DOD of my batteries. I came across images like this:


Which I thought might be useful. But then I noticed that when my batteries are being charged to Float state by my panels, the Victron app reports the max voltage as being about 14.5V, and min as 12.7/12.8. Does this mean min voltage is the more useful data point? This makes no sense to me because this is what the victron app is reporting now even though my batteries haven't made it beyond bulk charge for days.

Some screenshots incase this is helpful.



Less miserable weather:


Thank you all for any help offered,


jodusno1 asked
jodusno1 answered ·

2 Answers

Victron Lead Acid Batteries - Failure ?

All Victron batteries must have a manufacturing error after a lot of test and research on around 300 batteries from Victron mainly super cycle 25AH over 250 and 18 batteries Gel Deep Cycle 220Ah.

Most of the super cycle they fail within 6 months to 1 year even if you have them on float voltage and not cycling them, if cycling them on a solar system best you can get is 6 months. 30% got a catastrophic effect of swelling. Other manufacture of batteries with 4 year floating still there and running without a problem the only difference is that is 18Ah instead of 25Ah.

After 1year of using them new ones with serial numbers came out thinking they fixed the problem but at the end they all failed from 25Ah day one measured with a proper load tester they all end up at 3Ah the ones that are always on float voltage , the ones doing cycles are 100% dead. It was a big loss for us and there is no support or guaranty from our local dealer since they are not replying to our calls. They tried at the beginning to help but that didn't help since there is no response.

The 220Ah at a controlled environment at 25-30 degrees Celsius 70% state of charge as a discharge they get a half capacity if not less on some of them after 1 year.

After 1 year and 2 months it was failing cause of some of the cells in series of the 4 was actually close to 50Ah and some on 119Ah on 2 strings parallel of 4 in series.

All batteries show a good voltage like a new graph but with the difference of the capacity instead of 220Ah there new capacity 120Ah or 50Ah, on the small ones 25Ah when new but after 6 months to 1 year 3Ah if not swelling.

Note that internal resistance was measured but it can’t be trusted since it was showing good on a lot of cases but the capacity was not there, most test where done with C20 and C10 when new even C2 was good.

Hope this 2 year test and research on Victron batteries will help.

What is your experience with the Victron Lead Acid Batteries?

Alexandros asked
Alexandros edited ·

0 Answers

MIx AGM and LiFeP04

Serious question, please bear with me.

It seems that some boaters are supplementing tired AGM batteries with extra LiFePO4 batteries in parallel. My understanding is that this shouldn't be done. But I hear that many are pleased with the results.


Are there any gains?

Are there drawbacks?

Are they fooling themselves?

Are there any dangers involved?

kevgermany asked
northcaptain answered ·

7 Answers

Hybrid Lithium AGM setup

I am planning a battery upgrade for my new 4x4 which comes factory with a single 105ah AGM battery.

Due to space constraints I am planning to add around 100ah of LIFEPO4 prismatic cells to beef up the capacity.

All the loads i want to run are already wired off the AGM battery and I don't want to move all the circuits over to the lithium battery. The vehicle has a very complicated electrical system that I would like to leave as standard as possible.

So the plan is to have the lithium charging through a DC/DC while the engine is running, then when the engine is off the DC/DC will disconnect and the lithium will be used to charge the AGM as my camping loads slowly deplete it. In theory the AGM will stay at 100% SOC until the lithium is discharged. Then the lithium cuts out and I am discharging from the AGM.


I think this will work but welcome any comments, I'm a little out of my depth here.

The current plan is to use another, smaller DC/DC charger from the lithium into the AGM. Although looking at the voltage curves I wonder if I could save some money by switching to a cheaper DC/DC converter set at 12.8v, or even just a Victron Smart Battery Protect. With the battery protect only, the AGM should see a float charge of 13.8v from the full lithium, dropping down to 12.8v as it discharges. Then, I guess, they both both discharge together until the BMS cuts the lithium out at 12.0v. By which time the AGM is empty anyway and I need to run the engine or stop drawing power.

Is this reasonable? Or should I stick with a second DC/DC charger?

werdna asked
werdna answered ·

5 Answers

Victron SmartShunt does not detect charging

Hey, I need some help :)

I added the smartshunt to my second battery (Odyssey Extreme 34-PC1500) in my 4runner.

I use the REDARC DC to DC charging (BCDC1225D)

Everything works great except the app doesn't show the charging, but charging works and you can see life current on app but "stage of charge" only shows drops the procentage.

I think that battery settings maybe are wrong?

I attached the screen shot of my battery settings.


marekpawlik asked
pwfarnell commented ·

4 Answers

Battery Balance too many batteries?


I have 48 x 12v AGM 135aH batteries and have them configured in 2s 24p. (3 x banks of 8 2s 8p).

The batteries are about 3 years old (used in a ups system)(All wired in series).

The 3 banks are connected together with 25mm x 6m Bars bars with positive feed on one end and negative on the other.

When I set them up they we fully charge and with 0.05 of volt of each other. I have 4 85/250 mppt charging these with a Mutiplus 5000Va /24 running ESS.

i have 3 x victron battey balancers 1 on each bank. They where in alarm state

I have disconnected and metered the batteries today and the batteries are at least 1.2v out.I am planning to get them all back up to fully charged using external charger

Am i expecting to much to have this amount of batteries in series parallel. They have been working great over the summer but maybe the have been getting slowly out of balance.

The only thing that has changed is I have started using a scheduled charge overnite from the the last 3 weeks.

Any thoughts would be greatly received.

Many Thanks

richie-gorrod asked
JohnC answered ·

3 Answers

Temperature-CCA rates of AGM Deep Cycle Batteries

CCA rate of 165Ah AGM Deep Cycle battery is available only in 0°F / -17.8°C as 600A in datasheets. The Temperature-CCA characteristic of this model is required for my application.

The other products on the market can provide this graph.

Is there any available resource on this or any available official answer?

I just need to confirm that the CCA value between -5°C...+5°C.

Thanks in advance.

Melih Manisalıgil asked
Mike Dorsett answered ·

1 Answer

How low should AGM go daily and longer nights showing on Voltage graph.

I have a constant 12volt 1.45 amp load (so around 19 watts) 24/7 which does not alter at all.(runing all internet routers/ wifi etc direct DC)

I have a VE 100/30 MPPT powered by x2 250 watt panels in serious working well.

I am noticing my two 12v 110Ah AGM battries (in parallel) are lower each morning just before sun rise, I put this down to longer nights which makes sense. They are reaching float each day easily by lunch so seam nicely charged.(later on cloudy days but still making float)


My question is: what is the lowest we should take these batteries' voltage? I read around 12.00v is considered 50% so best to not go below? Agree?

If so plan to add a boost night time charge once I reach 12.00v pre sun rise.(looks like mid October To Feb this will be needed)

I am surprised though as my load being only 1.5amps (over a 12 hour night ) should only use around 18Ah and I have 220Ah (or 110Ah to get to 50% in theory) so def not getting the capacity expected or am I missing something?

Any advice? thanks

These are the batteries am using: (x2)


The supplier recommended these odd charge settings: (I ignored the float ones)


I am using MPPT Batt switch postion 2 (Green)


Thanks, its fun learning and having atleast something running offgrid.

simons-solar-studio asked
simons-solar-studio answered ·

2 Answers

Effective CCA of my Victron AGM batteries

I have a house bank of two 6V-225Ah Victron AGM batteries (BAT406225080) plus a starter battery for my boat. I just had a diesel mechanic tell me that I need to replace the starter battery. I'm able to turn my engine over, but when he load tested the starter battery it showed weak. I had the starter battery paralleled with my house bank though and my house bank is rated at 700CCA each (1400CCA total), so I'm wondering why that wouldn't have had an easy time starting the motor. I haven't tested my house bank for instantaneous load. I did load test them over 10 hours and was satisfied with the results. They're 6 years old and still powered a 7A load for many hours. My question is if it's normal for AGM batteries to lose the ability to drive an instantaneous load when they get old.

codefoster asked
sharpener commented ·

3 Answers

How much damage does a deep cycle do?

I have two 6V Victron AGM batteries (BAT406225080) wires in series. I recently had a failure on the circuit breaker for my battery charger, so my batteries weren't being charged and were run down to about 6V. Can anyone tell me bad that is for my batteries? I know it's not good, but is it more like "they likely need replacing" or "they'll be fine, just don't do that often"?

codefoster asked
najab commented ·

3 Answers

Electric Acting Up in Van

Hey there,

For the past few months the electricity in my van has been acting strange. Full transparency, I didn't do the buildout nor have a firm graph on the electric setup so I'll detail as best I can. (warning: it's a lot). Appreciate your help in advance!!

tl;dr - Electricity surges and drops overnight

Here is our setup:


(2) 6V Deep Cycle Batteries / 200 Amp Hour AGM battery bank (~3-4 years old)

12V 140 Amp Dual Battery Isolater - running off engine batter


  • (2) 275 watt Lg Solar panels
  • Victron SmartSolar Charge Connector MPPT 100 | 30

We're typically only running the main cabin lights, a Nova Kool R3800 Dc Refrigerator, Maxxair fan, and a small bathroom fan (only when bathroom is in use).

What's been happening:

- We first began experiencing what I'd call a 'surge' this Spring. The things mentioned above would be running fine then the lights would turn off/on rapidly, fan would turn off it is was in use (on if it wasn't in use), same for bathroom fan. This happened for 10 sec or so then repeat a handful of times. We typically turned off the fan breaker and turned off the lights until we needed them on again.

- On a trip last month, we weren't as much experiencing the 'surge' but instead woke up to water on our floor as our fridge defrosted overnight. This happened multiple times and the fridge struggled to function for the rest of the trip.

- We also had a few small water leaks in the van roof over the past few years. Only mentioning in case it sounds like a faulty wire (which I haven't yet seen).

- Lastly, the lights have turned on by themselves overnight. Outside of ghosts I can only imagine the system is turning on during a 'pulse'?!?


I've been doing more testing on the batteries. During the day (full sun), they're both tracking around 5.8-5.6v (per battery). In the early AM (around 6-7 before full sun), one remains around 5.8v while the other is lower at 4.6v. I have seen dips into the 8-9v when checking at night/early AM (which is the measurement for the 2 batteries combined). With full sun, we're typically 11-14v.

Lastly, I also noticed a quick drop in voltage around the pulses I've mentioned.


If you've made it this far in the post, thanks. Appreciate your time.

Is it as simple as I need new batteries or does it sound like something else is going on?

bridgeskd asked
marekp commented ·

2 Answers

ESS (extremely) slow charge

Hello community,

I have a Multiplus-II 48/5000/70-48 with AGM batteries

ESS is activated

when batteries are below min SoC, I can see the ESS #5 (slow charge in progress)

My issue is the **very** slow charge rate, 0.1 A max, usually lower...

Any ideas on where I could investigate ?



laurent-2626 asked
laurent-2626 commented ·

2 Answers

Integral question for freshly installed setup

Hello all!

I am looking for a piece of advice..

We have self installed this system with my dad. Advices and recommendations are very welcome.

The setup is as follows:

-2x SP 455W JA Solar Mono PERC (serie)

(VMPP): 41,82V

(VOC): 49,85V

-2x battery AGM 12V 300Ah Tensite (serie)

-MPPT 150V 35A Victron Smart Solar

My questions!

1) I would like to know if the following status info gathered from the regulator are okay for you.

2)are the settings right for the battery? There is a preset for agm spiral but I preferred to do this setup according to whats specific for the batteries.

3) would you comment on the equipment and tell me if there is something that makes no sense?


Image Caption


fran-parma asked
fran-parma commented ·

4 Answers

Victron AGM Peukert Value


Does anybody have the Peukert Co-Efficient value calculated by Victron for their AGM batteries? In particular the Telecommunications AGM batteries. I understand that this changes with the life of the battery but normally manufacturers provide a value. Thanks in advance for your help.


pmarine asked
Kees-Jan answered ·

3 Answers

What battery voltage should I auto connect / disconnect my inverter load ?

I'm sure this has probably been discussed before but cannot find a definitive answer...

I have a 650W off grid solar PV system with a Victron MPPT 100/20 charger, four 95Ah Exide AGM batteries linked as 2 x 24v pairs and a Victron 800W 240v inverter. I'm powering my computer servers, as they run 24/7, via a UPS that allows me to manually transfer the power connection from grid mains to PV power and back manually without interrruption. The computers are drawing ~250-300 Watts at present.

I'm building an automatic switch to handle the switching between grid mains and PV power, PV power having priority when available, else grid mains being connected. This has to be self contained due to its physical location.

I have an Arduino SBC monitoring the PV and battery voltages and currents, the plan being to use the Arduino to control the inverter remote on-off with a relay, hence causing the (remote) automatic power switch to connect the PV power to my computers when it's on and grid mains when it's off. I also have a Raspberry Pi running the Victron Venus OS.

I've been running the system for a couple of months, manually switching the power between grid mains and PV power based on the weather and data from the Arduino monitor and Venus OS.

I've trawled through endless notes and discussions and come to the conclusion that I should disable the Victron inverter when the battery voltage drops to ~24v on load, which seems to indicate ~50% battery discharge. I should re-enable the inverter when the battery voltage reaches ~26.0v on charge but off load. This appears to give me a sensible cycle between grid and solar power whilst attempting to maximise the life of the AGM batteries.

I'd appreciate any comments on this scheme from those much more knowledgable than me on this. I'm aware I can probably achieve this set up using standard Victron equipment but there's no fun in 'leggo electronics' :-)



paulm asked
paulm commented ·

1 Answer


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