Battery SOC diverging from Shunt SOC - eventual failure?

DIY
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1

In a configuration with…

  • 12v agm starter battery
  • 2x300 AH off brand lifeP04 batteries
  • 1x550w rigid solar panel
  • Victron Smartshunt
  • Victron 50/100 Mppt charge controller
  • Victron Orion XS 50a DC/DC charger

One of the batteries SOC is dropping over time and diverging from the other battery it is in parallel with and the SOC stated by the shunt. The voltages of both batteries match the SOC stated by the shunt. For example the lower soc battery states 37% soc but reports 13.27v while under load. The shunt reports 89% soc.

I am remote to the system and don’t have the ability to do a full charge and therefor a rebalancing on these batteries for a while.

Can anyone predict what will happen when the lower of the two batteries reaches a reported SOC of zero or close to it? The victron system isn’t tracking the battery SOC, but will the battery BMS shut the battery down or just keep on trying to charge. It does charge a bit each day, but not as much as the draw. Is there a chance the battery will be damaged?

The brand is GenholM and the manufacture isn’t very helpful right now.

Thanks for any input.

2

This is one of the problems of paralleling drop.in batteries. When you get to site you need to check that your cables are symmetrical and all connections made to the correct torque.

The SOC drift may be real, it may not depending on the accuracy of the current measurement. Most drop in lithium batteries work off voltage not SOC. When the voltage of the lowest cell reaches cut off the voltage the BMS in that battery will stop discharge bit will still allow charge so it should stop.it from going too low. Remember, you are asking on a Victron forum how non Victron batteries will work.

3

Remember, you are asking on a Victron forum how non Victron batteries will work.

Good point. Lots of experience in general here. I appreciate the comment.

When the voltage of the lowest cell reaches cut off the voltage the BMS in that battery will stop discharge …

This is re-assuring because, at least so far, the voltage reported is what would be expected for fully a functioning parallel setup. It discharges at night and recharges each day as would be expected. Just the SOC is slipping, so hopefully, as you say the BMS works off of the voltage not the soc.

Yes will check the parallel setup and give the a full 100% charge. If that doesn’t fix the SOC reporting from the battery and the voltage continues to be inline and match expected SOC from the shunt I may be tempted to ignore it.

Much appreciated for your thoughts.