On Fri, 1 Jul 2005 11:20:08 +0100, Michael Rigby-Jones wrote:

>...<
> >From the Energizer web site, and ignoring voltage drop over life:
>=20
> 1x Alkaline PP3 625mAh  Total energy =3D 14.4 Wh
> 2x Alkaline AA  2850mAh Total energy =3D 8.55 Wh

Is there a typo there?  0.625 x 9 =3D 5.625

> A PP3 has a significantly higher energy density than 2AA's

This certainly isn't true for rechargeables - a high-end capacity for a P=
P3 rechargeable is 250mAh (at 8V4,=20
giving 2.1Wh) whereas 1800mAh is at the low end for an AA (at 2V4 a pair,=
 giving 4.32Wh).  Granted that a pair=20
of AAs is bigger then a PP3, the capacity doesn't account for the differe=
nce.

> The downside is cost, 9volt "block" batteries such as the PP3 are signi=
ficantly more expensive than AA's.

Quite!  Looking at Tantronics site (http://www.tantronics.co.uk) at the t=
op of their ranges, a 250mAh PP3 is=20
=A38.50 (=A34/Wh), a set of four 2600mAh AAs is =A314.95, so say =A37.50 =
a pair (=A31.20/Wh), for 2.1 and 6.24 Wh=20
respectively.  If you can put up with only 1800mAh, four AAs are =A36.50 =
(=A30.75/Wh)!

I have seen an article proposing that the best use of rechargeables is to=
 use the largest single cell you can=20
get (D?) and a boost regulator... but that's for another discussion  :-)

Cheers,


Howard Winter
St.Albans, Herts



--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist