Karlos wrote:
The manufacturers could have chosen the half life of the cell to make it more obvious, but I doubt that a cell at 50% charge is not much use so they picked the 85% threshold instead.
Right. It's a matter of internal resistance. Most cell chemistries gain internal resistance as they lose capacity, decreasing the output voltage of the cell. At 50% capacity, your average alkaline battery would have an output of only 1.1-1.2 volts rather than the advertised 1.5, which is actually just not enough for some stuff. Their performance gets worse as they drain.
Incidentally, NiCd and NiMH don't have this effect (low internal resistance), which is why I like them. Pity they only have 1.2V even when fully charged, and they lose charge like fiends. And even worse, shops only sell padded crap like 2300 mAh NiMH D batteries (the theoretical capacity of an alkaline D battery is around 18,000 mAh, which should mean NimH D should be around 9000 mAh. These do exist, but they can only be bought specially and cost about £12 each!!).
Someone should do the world a favour and invent rechargeable batteries with 1.5V, low self-discharge and low internal resistance, but which aren't full of explosive ether like Li-Ion are. They'd be a rich man/woman!
Until consumer fuel cells came out that is... :-P
