William Sommerwerck wrote:
Probably not. The Norelco "charger" is probably little more than a
resistor
in series with the power supply. A NiMH should have no trouble with that.

As I understand it, the problem with this approach is the question of
shutting off the charge when the battery is full. NiMH cells are less
tolerant of being overcharged than NiCd, and are best used with a
charger that has a somewhat more sensitive full-charge detector (e.g.
zero-delta-V and/or direct temperature sense, rather than negative-
delta-V as was often used with NiCd cells.

This isn't a problem if you're charging at a fairly low rate. A good-quality
cell -- nicad or NiMH -- will tolerate an indefinite low ("trickle") charge.

I'd like to see a reference that supports that.

NiCd batteries are very tolerant of trickle charging.
Early NiMH cells were very INTOLERANT of trickle charging.
Lots has changed over the years. Maybe they're better now,
but I'd like to see some vendor info on that.



If the resistor is chosen to give a 0.1C charge rate when the cell is at
about 1V, the charge rate when the cell has "fully" charged will be rather
lower ("depending").

It's only in the past decade or so that rapid-charging with auto-cutoff has
become commonplace. Prior to that, almost every nicad device was charged
with a simple series resistor. And guess what? It worked.

Here's some empirical evidence.
Power tools have historically had three charge modes.
The cheapest have a trickle charger. People leave 'em on charge all the
time.
The "better" tools have a fast charger with a thermal coutout. The cell
gets HOT and the charge is terminated by the thermal cutout.

The "best" tools have a fast charger that often measures -deltaV for NiCds
or 0delatV for NiMH.

So, here's the experiment.

Go to a garage sale. Almost every garage sale has at least one battery
powered drill.
Have you EVER found a battery powered drill at a garage sale that had a
good battery? I haven't.

As I said earlier, I have a Polaroid #365 electronic flash with NiMH cells
that replaced the original nicads. The #363 rapid charger has no trouble
stopping and switching to trickle charge. It was designed almost 45 years
ago..

The bottom line is that you should always use the EXACT battery chemistry,
type, model number with the charger designed exactly for that battery.

If you're willing to reverse-engineer the charging circuit, you can often
use alternative cells.
Or you can redesign the charger to match the cells.
Or you can just get lucky with any random selection.
I've been lucky 99+% of the time. But I have also been unlucky.
One day I'll find the rest of the battery pack that exploded
when the lawnmower throws it thru a window.
YMMV