Gary Coffman wrote:
On Wed, 04 Feb 2004 11:42:25 -0500, Jeff Wisnia wrote:
Bob Engelhardt wrote:

We have a 9.6v Dustbuster that lost it's NiCd batteries rather quickly,
at least compared to the previous, lower voltage, Dustbuster. I have
ordered new cells to replace these, but I'm wondering about the
"charger" that the Dustbuster has. It's just a wall wart and a diode.
I.e., a trickle charger.

I seem to recall that trickle charging is not the best for NiCd's.
Right?

If not, I'm wondering whether I can use the "smart" charger that came
with my 9.6v Makita cordless drill. I'll need an adapter, clearly, but
is the Makita charger somehow specific to the Makita batteries, or will
it smart-ly charge any 9.6v NiCd?

IMHO continously trickling a nicad at less than 1/10th of it's
milliampere hour rating (i.e. less than 70 ma for a 700 milliamp hour
cell) does them no harm. You might want to measure the charging current
from that wall wart (after the cells are charged up) and if it is higher
than what I just stated, for the cell size in your Dustbuster, reduce
the current by inserting an appropriate sized resistor in series with
the charging circuit.

Overcharging a NiCd is *never* harmless. Overcharging can cause
voltage depression (often mistakenly called "memory"), and shortens
the life of the cell, even if it is at a "trickle" rate. It *may* not shorten
its life enough to matter if the trickle rate is really low (say 1/100 C),
but any overcharge is bad. You want to avoid it if you can.

In practice, overcharging at C/10 or so does not matter, if you do
not leave it on charge for weeks at a time.