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Dave Martindale
 
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Default AA battary capacity, Ah (?)

(Remove SPAM From Address to Reply) writes:

Please don't do that! Those cheap chargers are either constant current
or timer terminated.


That's partly correct. Yes, the cheap chargers are constant-
current, but no, they are not a problem. For most NiMH cells,
the "cheap" chargers are charging at a rate less than C/10, and
are no problem even if left plugged in all day.


There are two different types of cheap charger. They're both constant
current with no detection of end of charge. One type uses a low enough
charge rate that a full charge takes 14 hours; that's what you're
talking about. If the batteries start out partially charged, not
completely discharged, they will be overcharged - but at such a low
current that it won't hurt them.

However, the *timed* cheap chargers use a higher current that will
recharge the batteries in about 5 hours. They are a problem because
they will properly recharge *only* a specific capacity of battery, and
*only* if it's fully discharged before charging. If the battery is
higher capacity than the charger is designed for, the timer will shut
off before full charge is reached. If the battery is the correct
capacity but isn't fully discharged, then the charger will overcharge
it, and with a current large enough to damage the battery.

So, avoid the timed chargers completely. 14-hour chargers are OK but
slow. Fast chargers with end-of-charge detection are OK and fast.

Dave