Alex wrote:

"Gordon Henderson" wrote in message
...

In article ,
Timothy Murphy wrote:

(1) Does it really harm batteries to over-charge them?

What type of batteries? NiMH, NiCd, Sealed Lead Acid, Vented Lead Acid?

The answer is generaly yes, though.


(2) If so, where can one get a charger
that switches off when the battery is charged?

You need the right type of chrger for the battery type you are
charging. Usually you get them from the same place you getthe batteries,
or try Maplin, Rs, of TLC...


(3) How can one tell with a multimeter if a battery is charged?
Can one tell from the voltage?
If so, at what voltage would one say the battery needed charging?

You can't really tell with just a multimeter. A battery right off the
charger might well read above full voltage, but drain a little bit of
current from it and it might appear flat again. (Although lead acid
types are more tolerant of this test)


(4) Similarly, for non-rechargeable batteries,
can one tell from the voltage on a multimeter
if the battery should be thrown out,
and if so, what is the critical voltage for 1.5v batteries?

The critical voltage is the voltage at which your device stops
operating.

Different types of battery will behave in different ways - Old Zinc cells
and Lead Acid types will degrade gently through their life, alkaline have
a flatter discharge curve and Lithium even flatter, going from almost full
voltage to next to nothing in a matter of minutes (or less!) depending
on the application.

Sorry if this answer doesn't help much.

Battery technology is forever changing though, so who knows what will
come next year...

Gordon


Here's one for you - why do batteries on quality tools (nicad and nimh) seem
to go from almost full power to nothing very quickly, whereas on cheaper
power tools they gradually get slower and slower as their charge runs out?

NiMh. It runs out like a dog. Also cheaper batteries maintain voltage
less well under discharge.


Alex