Battery dying at half charge

[ballaw]

Hi, my battery has been dying at half charge for a while now. At first I thought it was because the reading was inaccurate and when I went to pedal assist level 5 a lot of current was required and the remainder was depleted quickly, but not it just dies well before the charge is depleted without being loaded hard.

Is there a particular problem this kind of symptom points to, the BMS or battery cells? The battery can be recharged just fine but always dies prematurly after about 1 hour of riding.

Another question I have, I opened the case the test the voltage on the batteries to see if I could get as lucky with diagnosis as this guy:

https://www.youtube.com/watch?v=KParyuK9pjU&t=1212s&ab_channel=Stevenc22

Unfortunatly the batteries all show a normal looking voltage. My question are the cells supposed to have different voltages? Most are 4.1 V but the last two rows are 3.6V

Thanks for any help!

[Roverdrive]

Have you tried balancing the battery?  Been reading up on batteries here and the Rad charger and BMS is supposed to bring low cells up to agree with the rest (assuming all are good) by leaving the charger running after the green light comes on.  Since you have access to measure individual cells try it and see if you can get those low ones up to 4.1

[DickB]

The groups of cells should all be at the same voltage. You have two groups of weak cells that are likely being depleted before the rest. When the voltage difference between cells is significant, the BMS shuts the battery down. The BMS is probably fine and doing its job. The low-voltage cells are bad. Balancing is worth a shot, but not likely to fix.

How old/home much usage on the battery?

[ballaw]

Hey, thanks for the help guys.

The battery cells are probably about 4 years old. Is that the typical lifetime? I can try replacing the low voltage ones and seeing what happens.

In the meantime how do I balance the battery as you said? I left them charging for over a week before I took it apart.