I'm a big fan of NiMH batteries (use a home made 5 cell 4.5AmpH pack for my
bike lighting commute). Your mileage may vary, but there are a few ways in
which NiMH seem to be more vulnerable that NiCd cells and which may give NiMH
an undeserved poor reputation. The main problem is that NiMH seem even more
sensitive to overcharging damage than NiCD. With both battery types, such
damage is permanent, though apparent partial recoveries are reported.
That means you want a "smart" charger with a very low (or no) trickle charge
after full voltage is reached. Most NiCD units are sold with cheap chargers
which just charge and charge, which is marginally acceptable with NiCD, but
less acceptable with NiMH cells.
Another point is the self-discharge rate of NiMH is higher than NiCds. So if
you let the cells sit around after charging, you may not experience higher
capacity. With both types of cells, you are best off storing the cells after
use without charging and then recharging the night before use.
Better for capacity and battery life.
Last point: please dispose of all cells (even alkaline) properly. Most US
residents just dump this toxic waste in the regular trash. Your community
probably has a place to dump these and you can store up a shoebox of drained
cells and drop it off there every few years...
Just charging along,
Eric Pederson
epederso@xxxxxxxxxxxxxxxxxxxx (no "n" in "epederso")
Professional home page:
http://logos.uoregon.edu/uoling/faculty/pederson/pederson.html
Personal home page:
http://darkwing.uoregon.edu/~epederso/
> Many ads I've seen state that "you can just keep using your nicad charger
> with NiMH batteries". The consensus on the list was to not charge the pack
> for more than 5 hours (after a big discharge) when using NiMH.
> I've accidentally left my NiMH test pack on the charger overnight. In the
> morning the test light won't go on and the pack doesn't work. After a
> while, the pack recovers by itself and everything seems to be back to
> normal. I don't know the affect of repeated overcharging though.
>
> John Hermanson
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