duff lithium ion ebike battery

[m3vuv]

hi all,ive just brought a 12ah 13s battery secondhand,it uses groups of 3x 26650 in series,i assume each cell is 4ah,the battery only manages i would say 5 amps output at most,the voltage drops under any load,full charge measures 56v,is there an easy way to test what cells are bad cell groups measure as follows: 4.123v,4.126v,4.127v,4.127v,4.126v,4.126v,2nd string:4.121v4.121v,4.003v,4.044v,4.122v,4.121v,4.125v,any idea how to test these to see if there all bad or just a few?,cheers m3vuv.

[Krisby]

Hello m3vuv, 

Just to get it clear in my mind, you have a 48V battery with 13 cells in series, but how many in parallel?  You mentioned a cell group of six cells, and a second group of seven cells, but I don't understand the configuration.  Can you please clarify how the cells in your battery are configured?

Cheers,

Krisby.

[shakalnokturn]

3P-13S
The sets down at 4.003 and 4.044V would be my first suspects of course, re-measuring voltages with some loading would give you a better idea.

Try bringing the 2 low groups up to the same charge as the others with an external charger then seeing how the battery deals with a load and how fast those 2 groups droop. If they perform like the other groups it's likely the charge balancing is bad.

It's also possible that only one cell of the 3 in those groups is weak, unfortunately the only way to test that is to break the parallel link.

[Gyro]

Double post... https://www.eevblog.com/forum/renewable-energy/testing-an-ebike-battery/

Make sure you're not your wasting time posting the same replies as others.

[shakalnokturn]

Bloody double posts... F. that... Best way to get either no or too much information. Anyway I'm not going round checking.

[m3vuv]

sorry,i made a cockup,there in groups of 6 cells,if one groupe is bad in the string will that groupe at like a big resistor blocking the current flow from the others?