In article ,
William Sommerwerck wrote:
It's important to match the capacity of nicad and NiMH cells, because
they have a very abrupt cutoff. This means that one cell can drop way
low, while the other cells are at a voltage high enough to continue
powering the device. If you let the device run long enough after this
point, the weak cell will drop to zero volts, then reverse, possibly
causing it to leak or explode.

Despite having used re-chargeable batteries from long before they
became a domestic item, I've never known one to explode. But then
I've always insisted on decent chargers.

I've never had the problem, either. But the charger has nothing to do
with it. I was talking about discharge (see above).

I've often run re-chargeables flat - although not intentionally. There'd
have to be a *vast* imbalance before one blew up. And indeed in practice
the cells don't all fail together, so even the very best makes will
exhibit just the effect you're talking about when old.

The safest way to handle a multi-cell battery pack is to run it until it
just begins to show a drop in performance, then charge it. This reduces
the chance of any cell being driven into reversal.

Yes.

The more cells in the battery, the greater the chance of reversal.

I've not actually experienced it. So put it in the same sort of pigeon
hole as memory effect. ;-)

--
*We waste time, so you don't have to *

Dave Plowman London SW
To e-mail, change noise into sound.