On Sun, 8 Nov 2009 23:24:14 +1300, Peter Huebner
wrote:

In article , Puckdropper
says...

Avoiding the charge/discharge/self discharge cycle would probably also be
a good thing. A decent charger could actually prevent such a thing
(There are conditioning chargers out there that discharge a battery fully
then charge it back up.)

I guess the whole point of this post is not to say the battery
technologies are bad, it's the charging systems. If we had more
universal batteries, I'd be willing to pay $200+ for a smart charger that
stopped charging when the battery was full, conditioned NiCds every so
often (might have to be a manual option), and generally took better care
of the batteries.

Puckdropper



Considering that I've used the top-of-the-line universal charger from
Panasonic that handles both nicd and nimh and several different voltages
automatically; and I've always removed my nicd batteries within a
quarter hour of their showing up as fully charged, I'd be surprised if
the charger was to blame. Still using it with my batteries that have
been rebuilt with NiMH technology since, and it works a treat. I top up
the NiMH every few months when I'm not using them, and they've lasted
much longer so far (I'm on the 2nd NiMH rebuild by now, b.t.w.).

The chemistry of NiCd and NiMH is very similar so the chargers are
very similar. The main difference is that NiCd shows a pronounced
drop in voltage as it completes charging (NiMH far less so). If this
phenomenon is used as a signal to terminate charging the charger will
over-charge and ruin NiMH batteries.

The other main charge termination method is temperature. Once a
battery reaches full charge, all of the electrical energy that was
used for charging turns into heat. If the charger uses this
temperature rise to detect charge termination it'll work well for both
battery technologies.

With either NiCd or NiMH you're better off not "topping up". These
batteries have a pretty substantial self-discharge and really want to
be stored flat (self-discharge is a safe way to get there). That's
not good for a tool that's only used occasionally and immediately,
obviously. NiCD or NiMH isn't the right technology for this
application either. It's a very poor choice for flashlights and
emergency lights and not used in UPSs for this reason.

The only other brand I've had experience of was my 7.2 Makita, a long
long time ago, and that battery (with a slow non-intelligent charger)
didn't last for too many cycles for me either before a disasterous
capacity collapse occurred.

Likely cooked the batteries. SOme of these "slow" chargers were
*really* bad.

My NiCD powered toothbrushes and D-cells on the other hand just keep
going and going and going for years because they get that regular
workout.

That's what NiCDs like. If you're going to charge them, let them
(self) discharge fully.

Well, that's the way I figure it, and it more or less coincides with
what I've read experts in the field saying. I'm certainly no expert in
accumulator chemistry myself.

I studied NiCd/NiMH and SLACs some time back because I needed them for
a product (and they guy before me blew it).