NMIH batteries - was: Re: HP 25 and HP55

From: Dave Dunfield <dave04a_at_dunfield.com>
Date: Thu Oct 21 20:30:48 2004

>>> -- I took apart the 25's battery pack and replaced the nicads with
>>> nickel metal hydride cells (the same ones I use in my camera)
>> Not a good idea. Nickle metal hydrides need different types of
>> charging. The won't last long with a NiCad charging circuit.
>I won't charge them in the calculator, they are regular AA cells so I
>can remove them and put them in a proper charger. :^)

Here's a question for battery guru's ... I have a gadget I built for
preventing "memory effect" in various nicad powered devices - mainly
ones like my Digicams which only discharge the battery 1/2 way (or
less) before complaining that the battery is low.

It is basically two springy metal bars which lets me put up to 10 AA or
C cells in parallel to discharge (I've got portable _at_M and 70CM rigs powered
by a C cell pack), an Ammeter, a low resistance, and a stud rectifier diode.

Basically, it draws about an amp from the cell when they are near fully
changed, and trickles down to nothing as they approach .7ish volts, and
never lets them go to zero.

I works REALLY well with nicads - I've got cells that I've been using in
my radios for many years and they still work very well (Prior to using
this, they would noticably lose capacity after a while)...

But: It doesn't seem to be quite as effective with NMIH cells ... they
still seem to be losing capacity ...

Any explaination, comments etc.?


dave04a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools: www.dunfield.com
com             Vintage computing equipment collector.
Received on Thu Oct 21 2004 - 20:30:48 BST

This archive was generated by hypermail 2.3.0 : Fri Oct 10 2014 - 23:37:23 BST