Re: Best recharable AA batts

Joe Kesselman <keshlam-nospam@xxxxxxxxxxx> wrote in
news:W-SdndG7qpP8N2rfRVn-uA@xxxxxxxxxxx:

><snip>Also, like most rechargables,
> they're typically 1.2V per cell rather than 1.5; some devices won't
> like that lower voltage. (This is also why you don't see as many
> rechargable 9V's; their actual voltage for six cells cells would be
> 7.2V, and I'm not sure they can squeeze in a seventh cell to bring it
> up to 8.6.)
>

Whether NiMH (or even NiCd) voltage is higher or lower than Alkaline per
cell depends on both the state of charge and the discharge rate. As
NiMH have substantially lower internal impedance than alkaline (and NiCd
quite substantially lower than NiMH), they actually provide higher
voltage at very high discharge rates once even half the capacity is gone
(this is why the digital camera folks with high drain rate during
picture taking find even modest capacity NiMH to give them more pictures
than Alkaline--by huge margins at the highest drain rates).

People actually do sell 9V NiMH with differing cell count, though the
labelling can be pretty confusing (right now, the higher cell counts
ones seem usually to get described as "9.6V", while the ones with one
less cell describe themselves as 9 or 9.2--these are _not_ comparable
numbers. If your application has relatively low draw rate, and may need
nearly the full voltage of a half-discharged Alkaline 9v, then you want
the higher-voltage lower-capacity model (though your are still stuck
with self-discharge times likely to be in the couple of month range when
new, likely deteriorating a bit with use).

As to sources, lots of folks have been buying NiMH from Thomas
Distributing for years. Here is their 9v NiMH page:

http://thomas-distributing.com/9v_nimh_batteries.htm

For lower prices but a much less established reputation (and much
narrower selection), I've had good luck with Amondotech. As of today,
their 9V NiMH page is:

http://www.amondotech.com/index.asp?PageAction=VIEWCATS&Category=266

I've recently bought their Titanium (brand) "9.6V" 180 maHr battery. I
charged it a week ago. Sitting unused since, it reads 10.3 V open
circuit today. For comparison, an unused (but several year old)
Duracell Alkaline 9V reads 9.3V open circuit on the same meter.

Amondotech offers quite good prices on AA NiMH. If you are a maximum
capacity freak, their 2400 mAHr "Titanium brand are currently $2.30.
But if you back off a bit in capacity to 1800 mAHr they are just $1.35,
with several other gradations.

For a non-mobile application charger, I've really like the Vanson
BC-1HU, sold by Amondotech for $24.95. It handles 4 batteries in any
mix of AAA, AA, C and D, and separates the batteries enough that the
AA's don't get nearly so hot as they do in comparable rate chargers in
the tinier form factors. Several hour charging times are prudent--I've
done visible damage to three brands of AA NiMH in a 1-hour Everready
charger, as the surface temperature at termination wrinkled, split, or
otherwise damage the surface coating.

One other thing to watch out for--fresh NiMH batteries brand new out of
the box may not give full capacity up to the first five cycles. They
also may behave oddly in a way which may fool "smart" termination
circuits of the sorts found in all fast chargers. So cycle them a few
times before using them, and watch them to assure your charger does not
cook them or quit after less than 10% of a full charge.

Good luck--I'm a commited heavy NiMH user for some years now.

Peter A. Stoll






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