My 3 year old GM 36V, 16Ah battery has been getting a bit lazy lately; I get only 25km out of one charge opposed to around 40km earlier, before the lvd cuts the power. The cell voltages are all within 0.02V of each other; both when fully charged, and after a 25km roundtrip. (Though, measured 1 week after the trip; the bms might have balanced the cells during that week of rest...)
Now, i'm very curious about most things, so I wanted to know why, so I bought an 'iCharger 1010B+':
http://www.jun-si.com/EnProductShow.asp?ID=93Primary made for the RC market; it's also an excellent charger for us nerds that want to know more, and control more...
![Grin ;D](https://goldenmotor.com/SMF/Smileys/default/grin.gif)
It has support for max 10 Lithium cells, and max 10A charge current. It shows you all cell voltages, and have multiple charging schemes and discharging schemes.
3 features made me buy it: 10A charge current, it can run from a 12V car battery, and it can show you each cell's internal resistance. The last feature are what really tells you the most about a cell's condition.
With a bit fiddling, I created an adapter to fit the GM's balance plug into the iCharger, and it showed me what I suspected; all cells had an internal resistance between 15 and 25 milliOhm, except one that measured 54 milliOhm...
(When I say 'cell' here, it means one group of 4 parallel cells inside my 36V/16Ah GM battery...)
So...
Even when cell voltage showed that all cells was equal and well balanced; one cell are probably not capable to deliver its voltage under full load anymore, due to higher internal resistance. So now I know...
![Grin ;D](https://goldenmotor.com/SMF/Smileys/default/grin.gif)
Now; i'm working on building a replacement for my gm battery, and I will write a story on that soon. All I will say for now is that it will consist of 24 LiFePo4 cells rated at 3.3V, 10Ah each, giving me a 40V, 20Ah pack.
![Wink ;)](https://goldenmotor.com/SMF/Smileys/default/wink.gif)