[PLUG-TALK] Rechargeable NiMH Batteries Question

joe at joseph-baker.com joe at joseph-baker.com
Tue Jun 14 21:37:19 PDT 2016

A voltmeter alone won't give you a totally accurate picture of the batteries capabilities.  As batteries age, they appear to have larger and larger output resistances.  The volt meter alone doesn't test the battery when it is supplying current.  
This will not be as noticeable as the effects that Russell has illustrated, but this is another reason to not use the lower voltage NiMH

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On Jun 14, 2016, at 8:31 PM, Russell Senior <russell at personaltelco.net> wrote:

>>>>> "Rich" == Rich Shepard <rshepard at appl-ecosys.com> writes:

Rich>    This is a question for all the electrical gurus here.  My clock
Rich> radio takes a pair of AAA batteries for backup when the house
Rich> electrical system goes off-line. A couple of weeks ago the unit
Rich> indicated the batteries needed to be replaced. I charged a pair of
Rich> NiMH rechargeable AAA batteries and put them in the clock
Rich> radio. The discharged battery icon continued to blink. So, I
Rich> recharged the batteries and found the same result.

Rich>    Replacing the NiMH batteries with alkaline, non-rechargeable
Rich> ones, turns off the icon, indicating that they're fully
Rich> charged. The NiMH batteries each read 1.39 or 1.40 volts so they
Rich> are fully charged.

Rich>    What might make the clock radio not recognize charged batteries
Rich> if they're NiMH and accept alkaline ones?

The normal voltage of a fresh alkaline cell is about 1.6V, which is higher
than a fully charged NiMH.  Also, NiMH are more likely to discharge over
time.  If the purpose is backup power, you are probably better off with
alkaline anyway.

Russell Senior, President
russell at personaltelco.net
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