On Mon, 30 Jan 2006 10:40:05 -0600, David Dyer-Bennet wrote:

[snip]

All my NiMH chargers claim to be able to charge NiCD batteries too;
are they lying to me? Or are there big compromises? This is
completely intellectual curiosity, since haven't used any AA NiCD
batteries in years.

Well, you really didn't provide enough information to say one way or
another. But chances are, you're safe as along as it says it supports the
battery type. My own high-end DC charger must be told the type of battery
it is charging, when it is charging in peak mode. I suppose it's possible
that a charger can automatically detect both types of fall-off but it may
run a higher risk of a false positive. Keep in mind, that's a guess on
my part. Assuming it's peak charger, a false positive would mean the
battery did not get charged to capacity.

If it is a trickle charger, a false positive/negative means it's either
over or under charged. And frankly, trickle chargers are well known for
over charging batteries. Over charging a battery can result in everything
from simple cell damage (reduced capacity and lower supported discharge
loads) to an actual fire. Also, don't forget that damaged cells may cause
a fire during high load discharge cycles too. Which is to say, an
undamaged cell versus a damaged cell, is more prone is be a victim of
excessive heat build up, during high load cycles. Lastly, "high load" is
largely dependant on both the type of cell. Remember, not all rechargable
cells are equal.

As a rule of thumb, given your cells, if your cells are hot to the touch
during and immediately after use, the application is probaly high load for
them. Likewise, if during charging, your batteries are getting hot to the
touch, long before the charge cycle is complete, you might question if the
battery is being over charged...especially if it's a trickle charger.


Greg