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E Z Peaces

wrote:
Some manufacturers warn that slow charging will damage NimH by
overcharging.

If left hooked up permanently as most people do then yes, any charger
can harm the battery.

I've read that slow charging will damage NiMH in a way
that increases the self-discharge. I've never slow-discharged NiMH, but
that drawback seems to apply to the NiCds I've had.

Slow discharged? I meant I've never slow charged NiMH!

Slow charging a battery until it's charged is preferred over a fast
charging a battery until it's charged. The heat generated by fast
charging degrades the battery over time when compared to slow
charging.

I felt that way until 1987, when I got a cordless drill with a C/2
charger. I thought that would be harmful to the cells, so I built a
regulator and set it to 1.4V per cell.

In a couple of months, two cells had severe self-discharge and the other
three had greatly reduced capacity. During slow charges of nickel
cells, salts accumulate on the plates. These salts can both reduce
available plate area and serve as conductors for electrical leakage
between plates.

Panasonic explains it in their tech manual for their NiMH batteries.

Nowadays there are chargers that will slow charge nickel batteries
without causing salt buildup. These chargers use pulses, like the
modern chargers designed to be left connected to lead-acid batteries.