On Sat, 13 Jun 2009 10:13:20 +0100, "Arfa Daily"
wrote:

Although the theoretical charging regime is not quite the same as for NiCds,
for all practical purposes, the same charger can be used without noticable
detriment to the performance or life.

The problem, as far as charging is concerned, is that the small
voltage depression at full charge that fast chargers rely upon for
detection of charge completion is smaller (about 30% of the NiCd
change) in NiMH than in NiCd. This means that NiCd chargers usually
miss it when charging NiMH and continue to charge until they time out
or they stop on thermal limiting. This damages the NiMH battery
irreversibly each time it is charged.

Using a fast charger meant for NiCd on NiMH will often damage the
battery being charged.

Slow (12 hours or more) chargers are not affected and will work on
either type of battery

The biggest advantage of NiMH types,
apart from the obvious size / capacity one, is that they don't suffer memory
effect, which is something that has always plagued NiCds.

Unless you are in space with a specific type of cell not found in
consumer applications and a rather unusual charge/discharge regime
memory effect does not exist in either NiCd or NiMH cells.

What does exist, and is mistakenly called memory effect, is voltage
depression caused by long term overcharging. This is somewhat more
severe in NiCd batteries than in NiMH but easily preventable.

This is of course
mitigated by the fact that the battery to be charged doesn't need to be
almost flat any more, because of the lack of memory effect.

There is no need to fully discharge either NiCd or NiMH before
recharge. Doing so has no beneficial effect upon battery capacity or
life.