Yet another internal resistance question...reading cells in a completed battery

[fuzzmunky415]

I've ordered a battery, and just saw a teardown showing the cells are laser-welded...so I suppose not user-serviceable. I also ordered a 1035+ with the hope of comparing the current state of cells in the pack wrt internal resistance, and to understand how well matched the prefab pack is. Then I thought to myself...self, how do I get an accurate reading when I cannot separate the cells? My first thought was to try my best to access reading from as close to the 'post' as possible, and since the IR meter is sending an A/C khz signal, I would need to access and remove the balance jumper from the BMS. Do I have this correct? Cheers!

 

[sunshine_eggo]

If the cells are in parallel, all you can do is measure the resistance of the parallel group.

Best to disconnect the BMS sense harness. IIRc, it's a ±1V 1kHz signal. Might piss the BMS off if it actually senses anything.

 

[robbob2112]

I assume the cells are 4s for a 12v battery?

 

[fuzzmunky415]

I assume the cells are 4s for a 12v battery?

Correct. I read between Snoob's lines, and gathered that. (that it will work for series)

 

[robbob2112]

With the battery disconnected you should be able to read the internal cell resistance of each cell. It will require disconnecting the balance leads for a minute but that isn't a problem.

The welds are directly to the battery posts so you can just put your leads on the center part.

 

[fuzzmunky415]

Eggcellent, appreciate your help! ('and the meek shall inherit the earth'....)