On Sat, 12 Sep 2020 00:59:04 +0000, Robert Riches wrote:

> On 2020-09-11, Martin Gregorie  wrote:
>> On Fri, 11 Sep 2020 13:10:31 -0400, Dennis Lee Bieber wrote:
>>
>>> My first was an HP-25, and the third was the HP-28 -- I don't recall
>>> if the latter is in storage or self-destructed; the 25 died when I
>>> couldn't get new battery packs (it was the only one I owned that could
>>> be used at work, as it lost its mind when powered down... Working in a
>>> black program is a pain.)
>>>
>> I discovered how to repair the HP-21 battery packs: split them open and
>> replace the pair of AA size NiCd batteries. The inner case is just
>> glued to the textured removable base of the battery compartment and
>> easily enough removed with a sharp knife.
>>
>> My latest effort, now that AA NiCds no longer exist, was more complex.
>> This time I fitted a pair of Perspex tubes as battery holders that each
>> take an AAA Sanyo Eneloop. These give longer runtimes between charges
>> and are still recharged by the original mains charger.
>
> Were the replacement cells NiMH chemistry?  For some applications, (Wahl
> series 4000 shavers, for example) a NiMH cell of the same physical size
> can replace the original NiCD cell, (as mentioned) the original charger
> still (at least the old high-current type) works, and the NiMH provides
> about 3X the shaves per charge compared to the original NiCD.
>
I should have popped the battery holder out before I wrote that: my HP-21
is actually running on Maplins Hybrid AAA cells.

I don't know the exact chemistry, but its possibly a riff on NiMH.

Its certainly not NiMH as we used to know it because it holds charge at
least as well as NiCD did, while NiMH was famous for self-discharge: the
ICG flight logger in my glider uses a pair of AA size NiMH and *must* be
recharged every 1.5 - 2 months when its in use during the winter.
Otherwise the batteries will self-discharge and destroy themselves.


--
Martin    | martin at
Gregorie  | gregorie dot org

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