Could I even leave them in the nicad charger to stay fresh?

No. I wouldn't do this unless the charger were specifically designed for it.

NiMH cells show a voltage drop at full charge -- and require a heavy charge
to reach that point. It's unlikely a nicad charger would shut off at the
right point.

You're right. Although NiCd cells do have a voltage dropoff at full
charge, it's more pronounced than in a NiMH. A charger originally
designed for NiCd cells may wait until the voltage drops off
significantly (negative-delta-V) before terminating the charge. By
this point, a NiMH will have been significantly over-charged, which
isn't good for it.

NiMH battery manufacturers tend to use a dual cutoff approach - shut
off when the cell temperature starts rising, or at zero-delta-V.

I don't think NiMH cells are bothered by a trickle charge.

Depends on the charge level. A slow-charge rate (say, C/10 or C/20)
in an "overnight" charger may overcharge the NiMH cell if left
connected indefinitely.

A very low (e.g. C/100 or so) charge rate seems to be safe, I gather,
but it's also rather ineffective for NiMH cells - they have a poor
"charge acceptance" at low charge rates, and most of the power just
turns into heat.

The battery manuals I've read say that if you do decide to use a
maintenance charge (to keep the cells charged up indefinitely), what
works best is a pulse-charging technique. Hit 'em with a brief pulse
of current at a high rate (C or C/2 or so) every once in a while, and
let them rest between pulses. Time the pulses so that the total
charge delivered averages out to around 1-2% of their rated capacity
per day. This should keep them topped up (countering their tendency
to self-discharge) without overcharging them.

You should get NiMH cells with at least 2500mAh capacity. They're not
expensive. I also recommend the Maha/Powerex MH-C9000 charger.

For batteries which will be charged up, and then discharged heavily
within a few days to a week, that's good advice. Ditto if you're
planning to keep them hooked to a properly-designed maintenance charger.

For batteries that you're planning to charge, and then leave on the
shelf (or in equipment) for weeks at a time, I think it's better to go
with the new style of "ultra-low self discharge" NiMH cells - Sanyo
Eneloops, or Powerex Immedions, or Hybrios, or types of that sort.
Their rated capacity is lower (2000-2100 mAh), but unlike the older
style of NiMH they'll hold most of their charge for months.

I second the recommendation for the MH-C9000. A very neat piece of kit.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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