> > When considering 9V , AA and AAA batteries .... does one get the best
> > bang for the buck with .......
> > primary alkaline
> > primary NiMh
> > secondary NiMh

YMMV.
E&OE.

AA has about 2+ x AAA capacity and are often of similar price.
AAA are generally an abomination unless small size is an essential.
AA with boost converter will usually give better energy/$ and energy
volumetric density than AAA.

Alkaline AA have ratings hardly more than the latest top NimH.
Generally under 3000 mAh in each case, so far.
NimH have a better sustained high current capability.
Various magic technologies may give primary Aa cells more current
sustainability but the mAh seems little affected across Alkalines and
consumer "Lithium" cells.

This is a retail reseller page but gives a good idea of available
primary Alkaline mAh capacity at different sizes from one maker
(Eveready).

=A0 =A0 =A0 =A0 =A0 http://www.batterycountry.com/ShopSite/alkaline-batteri=
es.html

Eveready have far far more data available but it's not usually all in one p=
lace.

When it comes to serious AA use, buying NimH is the overwhelmingly
most cost effective choice wrt Alkalines.
NimH cycle life is often said to be 500 cycles but DO read spec sheets
to see the conditions.
Under deep cycle use "rather less" may be achieved.
Under light depth of discharge rather more.

LiIon cells are nominally 3.6V.
They CAN be had in AA / 14500 form factor.
Some people use these with a spacer to give the voltage of 2+ x Alkalines.
Alkaline Voc new is 1.55V.
LiIon needs special chargers.
Using them bare in place of AA's is living dangerously. ALL LiIon
should have inbuilt protection circuitry but some AA do not for
certain. Even some 18650 do not but that is less common.
"Vent with flame" is a significant risk with unprotected LiIon.
And a risk with protected LiIon.

The new great hope is LiFePO4 / Lithium Ferro Phosphate.
About 3.2V means terminal voltage.
Volumetric energy densities maybe somewhat above NimH.
Cost should be 2 +/- 0.5 x NimH price but actually vary quite widely.
4 x 400 mAh LiFePO4 could be had at Walmart for $US10 a while ago.
Claimped AA LFP capacity is often 600 mAh but probably more like 500
mAh and can be lower.
Anything out of China of no-name type can be MUCH lower at any stage.
LiFePO4 can be superb and terrible depending on maker.
18650 LiFePO4 cell is about 1100-1200 mAh typical and maybe a bit more
but not much. Anything marked eg 1400 mAh is suspect for capacity so
probably for other things as well.
Special charger needed. Similar to LiIon but with differences.

> > I have seen AA LION batteries advertised. =A0How is this possible? =A0I
> > thought LION was 3.6V.

As above.
Yes, it is. So ? :-)
ie don't use on 1:1 basis. DON'T charge in std charger.

> If one wants to keep all the battery powered toys going , what is the
> best choice now ?

AA NimH usually. Reputable brand.
As others noted - SOME devices need Alkaline voltage levels and NimH
may be too low.

Some people are using LiFePO4 AA + 1 spacer to replace 2 x Alkaline AA.
Max voltage may be a bot high but most products don't care.
LiFePO4 will discharge to 2V safely typically although higher is kinder.
Lower is not recommended. Cells should have internal protectors BUT
far less dangerous than LiIon.

> Are cheap batteries from China going to be a safety issue ?

Most batteries come from China.
Cheap ones MAY be good. Or not.
Bad Alkalines are usually just low performance.
Bad NimH will usually not burn etc too too often or much.
Bad LiIon may be fun, depending on what they are in when they go bad.

NimH goodness can be sort of checked [tm] by weighing or, lacking
scales, by "hefting" in hand. Similar specs from different suppliers
should weigh similarly. Low weight is usually an indication of junk.
Alkalines also should weigh similarly to each other.

NiCd weigh somewhat heavier per mAh than NimH. A 'nice and heavy' for
the size but low capacity NimH may really be a NiCd.

For toys self discharge / shelf life doesn't usually matter much. NimH
rate is highish but has been getting better for some years.
If it does matter then newer low-self-discharge NimH are available.
Firstish was Eneloop but now there are many brands. The actual
technological cost of doing this is low (mainly a thin coating of
Copper on Ni powder during manufacture AFAIK but I may well be wrong)
- I'd expect this to become the NimH norm in a few years.

IF you have tight control of battery replacement and charging then
LiFePO4 is liable top give the cheapest per cycle cost battery over a
long period. I'm about to do some serious playing with them ... :-).


=A0 =A0 =A0 =A0 Russell McMahon

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