Mel Evans wrote:
> Subj:   3V cell in AA size

Lithium coin cells are worth looking at, as they are relatively low
cost.

The CR2032 (20mm dia x 3.2mm thick) has a capacity of 220 mAH, which is
25 micro-amp years.

Regarding cost: W H Smith (a large UK shop chain) sell the CR2032 at UKP
2.69 (4.3$), which is outrageous. They can be bought for half of this,
and a look at Trade catalogues shows them priced under a pound.

Reliability: coin cells have a type of seal known as "crimped", and has
a recommended life of around 5 years. For the highest reliability (10
years), "laser-sealed" cases are used, mainly on cylindrical cells. Many
brands of cells use Sanyo patents for the seal (and no doubt for other
chemical features).

Current Drain: Varta (for example) recommends a max continuous drain of
3 mA.

I was given a tiny Chinese FM radio (for cycling use). It uses a CR2032
and consumes 12.8 mA. The cell supplied was by Maxell. The radio gave up
after 3 hours. Its voltage is now 2.4 volts (initially > 3V), and it
hasn't recovered. A pity. This radio is cheap, neat and useless. I shall
be fair to it and try a new cell. Meanwhile it's back to the Walkperson,
which is huge, but cheaper to run.

John Blackburn,
South London UK.