Sudden Drop in EG4 24V 200AH Battery Capacity After 0% SOC Discharge and 29V Charge

Apica

Hi everyone,

I’m running an open-loop system with two (2) EG4 24V 200Ah LifePower4 batteries connected in parallel using busbars inside an EG4 battery rack enclosure. Over the past few months, I’ve noticed a gradual but consistent decline in the reported capacity—about 0.2Ah lost weekly.

Here’s my charge profile:
Bulk/Absorb: 28.0V
Float: 27.0V
Rebulk: 26.4V

These batteries were used individually in two separate systems for about a year before I reconfigured them into the current parallel setup in March this year. At the time of installation, their capacities were 196Ah and 198Ah respectively.

I’ve been monitoring both batteries regularly using EG4’s BMS_Test software. Two days ago, I noticed their capacities had dropped to 188Ah and 196.20Ah. After reaching out to Signature Solar, I was advised to discharge both batteries down to 0% SOC and then charge them back up to 29V.

I followed those instructions yesterday. However, once the batteries hit 0% SOC, their Full_Battery_Capacity immediately dropped to 181Ah and 181.20Ah. I began recharging each battery individually at 29V. One battery is now fully recharged at 100% SOC, but the Full_Battery_Capacity still shows 181Ah—no improvement after the overcharge.

Below is a screenshot from BMS_Test software showing the current state of one of the batteries after this process:

As you can see, the voltage spread across the cells is concerning, with Cell 7 sitting noticeably lower at 3.395V compared to the others, which are mostly in the 3.49–3.51V range. Max cell voltage difference is 0.119V, which seems significant at full charge.

At this point, I’m really concerned about this ongoing capacity loss and unsure how to proceed. Has anyone experienced similar behavior with EG4 batteries or know what could be causing this? Any advice would be greatly appreciated.

Thanks in advance!

Dave Angelini

How long did you hold at the absorb point?  On open loop and even some closed loop systems you need to hold at the set-point long enough for the BMS to balance the cells. In other words do not be fooled by 100% Soc. Give the cells enough time to balance. This is even more important with different age banks or unequal wiring of the banks.

Apica

When using a Bulk/Absorb voltage of 28.0V, I typically set the absorb time to 15-30 minutes. However, at 29.0V, I reduced the absorb time to just 3 minutes, which is the minimum allowed on the Midnite Classic 150. According to Signature Solar's tech support, it's best to either disable absorption entirely or use the shortest possible duration, as these EG4 batteries don't respond well to extended absorb cycles.

littleharbor2

Does your system have a Balance on charge only setting? Some BMS have the ability to only balance while charging or balance all the time if you disable the balance only while charging, your battery should balance out eventually. Once they get balanced you can set it back to only balance while charging and see how it goes after that.

Dave Angelini

You have to get them balanced ! They may be damaged also.  Tech support can very often miss the point. They often read from scripts. Some are very good also.

JRHill

Dave Angelini said:

You have to get them balanced ! They may be damaged also.  Tech support can very often miss the point. They often read from scripts. Some are very good also.

Boy, isn't that the truth.