In message , Hank
writes
Could I be right in thinking that using a battery charger to recharge a
run-down car battery tends to reduce the life of the battery? On more
than a couple of ocasions, car batteries I have owned have not survived
long after I have used mains plug-in chargers to recharge them.

The reason the batteries needed charging was not due to any fault in
the battery; it was due to the cars having ben standing, undriven, for
a long time.

Lead acid batteries are easy to destroy. They do not handle deep
discharge well and suffer from sulphation of the lead plates inside.
This is where an insulating layer forms on the surface of the plate
reducing it's ability to do it's job.

It follows that it's best to keep them topped up from time to time, but
slapping one on a cheap charger that just pumps current in constantly
will also result in damage, particularly if the acid/water level inside
isn't monitored and is allowed to drop below the top of the plates.

Care of batteries that are not being used for a while is a mix of
occasional top-ups and a bit of discharging too. You can get devices
that apparently condition the battery by pulsing a brief high current
load across it while it's on a charger.

It's a complex subject!

--
Clive Mitchell
http://www.bigclive.com