Re: [NTLK] Constantly charging NiMH batteries

From: Gruendel, Frank 3837 PPE-S3 (Frank.Gruendel_at_de.heidelberg.com)
Date: Wed Aug 29 2001 - 12:48:07 EDT


>> When I'm not using my Newton 2100s, I have it plugged into the power
adapter
>> which charges the NiMH battery I got from Battery Technology so that I
can
>> always have the 2100s at full charge when I am out in the field. Is this
a
>> bad thing where the battery is concerned? I had thought it not to be a
>> problem since NiMH batteries are supposed to be free of the
hysteresis/memory
>> effect that plagues NiCd batteries? Thanks.

> Last I've read on the subject (Frank, you correct me if I'm wrong ;-) is
> that they don't have memory effect *as bad* as the NiCADs, but they can
> develop some more or less serious memory effect if you always recharge
them
> before they're drain out. If you completely drain them every once in a
> while, they would probably keep their charge longer.

This is something I can't really prove as you find different opinions on
that
depending on which book you read or which "battery guru" web site you surf
to.

Fact is that *most* books say that NiMH batteries generally do not suffer
from the memory effect, often followed by a statement like "at least not
to the extent NiCads do" or something like that. I'm not sure if anyone has
ever really proven this assumption by taking a sufficient amount of battery
sets,
always discharge one part fully and another part partially and after a
couple
of dozens of discharge cycles compare the two parts' performance.

Fact is also that all kinds of rechargeables have a limited number of
charge/discharge cycles. NiMH have significantly less than for example
NiCad's.
Again, depending on which book you read you will find different opinions on
the definition of a discharge cycle, some say that discharging a batt to
90%, then charging it to 100% is not a full cycle, but only 1/10 of it.

My personal opinion and experience is that one should try to discharge all
kinds of rechargeables as much as allowed. The value of "allowed" depends on
the technology, of course, but the Newtons usually see to it that batts
aren't discharged deeper than they should, provided you don't trick them
into
believing they are powered by a battery type that in fact isn't there.
The exception to this rule are rechargeable alkalines. Their performance
depends on how soon you recharge them. They'll work longest if you recharge
them frequently, the more you discharge them, the shorter they'll live.

Frank

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