Batteries shutting down long before capacity is consumed

[GrandAdventure]

I am absolutely stumped by what’s going on, and need some help. Please understand that I only have enough knowledge to be dangerous, so please keep any replies basic so that I can fully understand.

By way of background, my RV’s system consists of a Victron MultiPlus-II 2x 120V 12/3000, a Victron SmartSolar MPPT VE.Can 150/100, a Victron BMV-712 Smart Shunt & Battery Monitor, 1200 W of solar, and 500 Ah of LiFePO4 battery capacity in a bank of five 100 Ah Battle Born batteries. At one time, the battery bank had six of those Battle Born batteries, but earlier this summer I started having issues similar to what I’m about to describe below, and I thought that I found one battery with a questionable BMS, and removed it from the system. At the same time, I cleaned up my battery bank to tie each battery separately and directly to 600A bus bars, with the cables all as short as possible (24”) and of equal length. I’ve since been on hookups most or all of the time, so I haven’t until now really had the chance to see what difference removing that battery made, until now.

We arrived at this dry campsite on Sunday afternoon. I was awakened by a low voltage alarm from the MultiPlus-II at 4am Monday morning, just before the batteries shut off, too, due to low voltage. Going into the VRM to try to see what happened, SOC showed 62% at the time of shutdown (of course, the shunt calculates SOC based on amp-hours consumed), yet voltage had dropped to ~ 10V.

I chalked it up to forgetting to switch the absorption refrigerator from AC mode to propane. At this time of year I’m barely peaking over 500W of solar from my 1200W system, so on Monday night I topped off with the generator, barely reaching absorption before having to the generator off when generator hours ended at 8 pm. I awoke yesterday morning to 67% SOC and ~ 12.8V (of course, under load), so I assumed all was good.

Last night, I again topped off with the generator, barely reaching absorption by the end of generator hours at 8pm.

I awoke this morning at 7:45 a.m. at 66% and ~12.8V (again, under load). I brewed some coffee and started working. Once the coffee maker finished the battery monitor showed 12.60V and 66% SOC. What I need for work creates an AC load on the MultiPlus-II of just over 200W. It seemed to be a similar situation as the day before, so I thought little of it. The rising sun wasn’t yet high enough to produce enough power to exceed consumption, so I was still slowly discharging. Just now at almost 9am, I was startled when the low voltage alarm went off and the MultiPlus-II shut down due to the low voltage. I checked the VRM and the batteries showed 62% SOC and 10.2V when the low voltage alarm went off.

So, it’s always happening at around 62% SOC as calculated by the shunt, which is after I’ve consumed only ~190 Ah of a 500 Ah battery bank. At around 65% SOC the voltage plunges from around 12.55V (again, under load) to barely over 10 V.

Help!!

[pwfarnell]

Have you adjusted the BMV settings particularly the charged voltage. The default setting with solar charging, (especially at lower light levels) can result in the SOC synchronizing to 100% before the batteries are full. Have you also reduced the capacity to 500Ah. The attached FAQ covers the correct settings.

A second FAQ covers wiring, the chassis connection is often a source of errors on RVs and boats resulting in some loads not being measured, so the batteries run out quicker than the SOC suggests.

Are your batteries balanced, hopefully you have Bluetooth batteries so you can see individual cell voltages. An unbalanced battery will display as 100% SOC before it is full and have low voltage before the SOC says it is empty. Unbalanced batteries have a lower effective capacity than nameplate. Cold batteries also have lower effective capacity.

Battery monitor jumping to 100% or reporting a high SOC with low Volts / the BMS shuts down

This topic covers the reported SOC being out of sync with the actual battery voltage or state. It covers BMV battery monitors, SmartShunts, Lynx BMSs and Lynx Shunts and will just be called shunt below. It is also assumed that the shunt is monitoring the domestic / house / cabin battery bank and not engine start / bow thruster / winch / caravan mover battery banks. The problems may be one or more of the following and is often linked to mobile applications with small solar systems. The SOC jum…

Shunt / battery monitor not reading the correct SOC/ Amps, missing solar, decreasing daily or other misreading problems

This topic covers the SOC / Amps reported by BMV battery monitors, SmartShunts, Lynx BMSs and Lynx Shunts and will just be called shunt below. It is also assumed that the shunt is monitoring the domestic / house / cabin battery bank and not engine start / bow thruster / winch / caravan mover battery banks. The problems may be one or more of the following The SOC decreases daily despite the solar charger or other charger(s) working. The SOC increasing when discharging and falling when charging…

[GrandAdventure]

@pwfarnell

Have you adjusted the BMV settings particularly the charged voltage. The default setting with solar charging, (especially at lower light levels) can result in the SOC synchronizing to 100% before the batteries are full. Have you also reduced the capacity to 500Ah. The attached FAQ covers the correct settings.

A second FAQ covers wiring, the chassis connection is often a source of errors on RVs and boats resulting in some loads not being measured, so the batteries run out quicker than the SOC suggests.

Are your batteries balanced, hopefully you have Bluetooth batteries so you can see individual cell voltages. An unbalanced battery will display as 100% SOC before it is full and have low voltage before the SOC says it is empty. Unbalanced batteries have a lower effective capacity than nameplate. Cold batteries also have lower effective capacity.

Thanks for the help! Yes, the BMV settings are set for a 500 Ah battery bank, have charged voltage set at 13.4V, and on Monday night after topping back off with the generator I reset SOC and synced SOC to 100% using VictronConnect. Both the MultiPlus-II and the SmartSolar are grounded directly to the trailer frame.

Unfortunately, those batteries aren’t equipped with Bluetooth capability so I can’t observe individual cells. The batteries should be well balanced as they’re hooked up to bus bars via the method described above, and we’ve been on electrical hookups for several months since I rebuilt the battery bank that way, so the MultiPlus-II would have fully topped them off and was trickle charging through the duration of each week-long stay. Temperatures here where we currently are along the central California coast are inconsequential, with highs in the 70s and lows in the 50s. We had similar temperatures in Canada this summer when this problem first reared its ugly head.

[chicagoandy]

@GrandAdventure

BMV settings are set for a 500 Ah battery bank, have charged voltage set at 13.4V, and on Monday night after topping back off with the generator I reset SOC and synced SOC to 100% using VictronConnect. Both the MultiPlus-II and the SmartSolar are grounded directly to the trailer frame.

It sounds like your batteries are badly out of balance. That will cause them to shut down after only consuming less than their full capacity.

BattleBorn Batteries are primarily ‘passive balanced’. This means they must be charged regularly to 14.4v and held there for a good amount of time. BattleBorn recommends charging to 14.4v at least once a week to keep them in balance.

FAQ: Will I need to periodically balance the batteries? l Battle Born Batteries

[GrandAdventure]

Thanks Andy. Given that I’ve been on hookups for the past several months, and therefore the batteries have been maintained at 100% and trickle charged while on hookups, not to mention that the solar controller is always on too, I’m assuming that they’re effectively passively balanced because they’ve regularly gotten up to 14.4V.

In the way that my battery bank was previously configured, some of the battery cables were of an uneven length (although not horrifically so), and they were connected in the conventional way in parallel from one to the next. Perhaps that put them out of balance? Is there another way for me to balance them?

[chicagoandy]

What is your battery charge bulk/absoption charge voltage set to?

You’ve described balancing between the different batteries, but batteries also need to be balanced within each battery. The actual cells themselves will fall out of balance. I think that’s your problem

[pwfarnell]

@GrandAdventure

Thanks for the help! Yes, the BMV settings are set for a 500 Ah battery bank, have charged voltage set at 13.4V, and on Monday night after topping back off with the generator I reset SOC and synced SOC to 100% using VictronConnect. Both the MultiPlus-II and the SmartSolar are grounded directly to the trailer frame.

If you read the FAQ and you charge to 14.4V then your charged voltage should be set to 14.2V to make sure it synchronises only when the batteries are full. 13.4V is too low and could give false synchrizations.

[GrandAdventure]

Bulk and absorption are both set to 14.4V. Float is set to 13.6V.

[GrandAdventure]

IIRC my charged voltage was set to 14.4V in the battery monitor prior to Monday. I only dropped it to 13.4V after Monday’s overnight incident.