LIFEPO4 battery charge/discharge performance issues

[m_abukhalid]

Hello everyone,

New to the forum and hope that someone can help me get some direction on my recent issue. I am trying to decide the meaning of the issues I am having with my new 12V 4 cell 80ah LIFEPO4 battery that I purchased of Aliexpress and how to best proceed while Im still able to dispute the purchase. It came with an 80a BMS with bluetooth capability and Ive been using a bluetooth app on my phone to monitor performance. I have done 4 cycles on it so far and currently the best I have seen out of it is about 55ah. When charging, the voltage difference between cells is within 0.004V. As the voltage at cell 1 gets close to 3.4V, that cell starts to charge much faster than the others and the overvoltage trips as cell 1 exceeds 3.6V while the other 3 cells are still barely registering 3.4V. During discharge, the voltage difference is solid to within 0.003V and as cell 4 approaches 3.2V, it drains much faster than the rest and undervoltage trip is activated as cell 4 reaches 2.67 voltages while the other 3 cells are still around 3.1V. The max voltage Ive been able to charge this battery to is 13.8 which quickly levels off to 13.4 as the BMS drains the overcharged cell (1). The min voltage Ive drained it to is 12V.

I see the BMS "balancing" the higher voltage cell during charging once its voltage exceeds 3.4V but I wonder if its working. Anyone have any idea how to best investigate or resolve this?

Daoud

 

[DThames]

Have you considered charge and discharge tests on each cell, one by one? This would allow you to single out a bad cell without any confusion.

 

[m_abukhalid]

Absolutely, but that would involve taking it apart (removing the blue seal wrapped around the battery) which would void the warranty. This would be much easier if I had gone the DIY route. I am wondering if using a low power balance charger (eg. 50W Tenergy TB6-B) to try to resolve the issue. Since Im overcharging on Cell 1 and getting undervoltage on cell 4, its almost like the BMS is just not doing anything .

 

[DThames]

Absolutely, but that would involve taking it apart (removing the blue seal wrapped around the battery) which would void the warranty. This would be much easier if I had gone the DIY route. I am wondering if using a low power balance charger (eg. 50W Tenergy TB6-B) to try to resolve the issue. Since Im overcharging on Cell 1 and getting undervoltage on cell 4, its almost like the BMS is just not doing anything .

Sorry, I misunderstood. I didn't understand it was a purchased assembled battery. In the dispute process they want photo proof. Can you capture photo evidence that one cell is causing the premature discharge cutout and premature charge cutoff? Photos of meter readings might work of documented well. If the seller is not willing to resolve, Aliexpress will settle it. Try to make a clear case that anyone can understand. Less than stated capacity shown and evidence of a clear cause should make your case.