I would suggest doing as mentioned above, equalise the cells on a board and then charge to maybe 1000mAh capacity before storing. If cells are being measured at 0.05V then they have an internal short of some sort which is depeleting the capacity faster than the other cells which are OK. This is not really a good thing as these cells will always lag behind the other in the pack, will not reach top of charge and will be over discharge in the next cycle which can mean those cells are driven negative and can vent... it becomes a downward spiral...
Never store your NiMH cells at voltages of less than 1V as this leads to permanent capacity loss due to internal cobalt migration (its a bad thing).
The crunch with these high capacity cells is life, you dont get such high capacity and voltage without trading something.. in this case (i) cycle life, (ii) reliability and (ii) self dischrage rate. Everyone wants the big number on the cell, and that is fine, but you wont get as good all round performance as you would with a Sanyo 2600mAh cell.. which would be good for 1000 cyles. (2600mAh you cry, how crap is that... maybe, put Sanyo have just launched a new version of it and I would want that in my cordless drill any day!)
I sell GP4300 cells and they are very popular, but you cant expect them to last forever.. its a case of the candle that burns twice as bright burns half as long (or something like that!).
As for the -dV question, I would personally use 5mV per cell. (30mV/pack) but this is a question of personal prefference - they longer the amount of overcharge the higher the higher the temperature and the shorter the life.
One last point. If you ever buy cells from a shop, before you do ANYTHING (in fact, do this in the shop!)... measure the voltage of each cell, if any are <1.0V give them back. If 5pcs are 1.20 V and one is 1.1V give them back. I am not saying that this has any indication on capacity because it does not, but the one cell that has the lowest voltage will die first. I would put money on it!
N
rant over..
29-12-2006
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