I visited the Great British Inventions Fair last weekend and got some
good ideas about batteries.

Other devices on view included the Talking Potty (slogan: "the Potty
that praises the Botty"), the Floating Doorstep Anti-Flood device, an
entirely flat PC, thief-proof concrete loud-speakers, nuclear-powered
bicycle, multi-function adjustable rod, Perpetual Motion Mechanism that
generates 71 horse-power from 12 tiny springs (not working, apparently
due to poor spring quality), device for applying insecticide to a cat's
backside as it passes through a cat-door, etc etc.

There was one really interesting booth, where a man had a really good
product concerned with solar recharging of lithium secondary cells. His
background is the security industry. He has a deep knowledge of
batteries and has spent a couple of years doing extensive tests on all
types of rechargeable cells.

Two of his conclusions seem worth passing on. The first is that he finds
that the so-called "memory effect" in NiCads is also present in NiMH
cells, which he believes to be stronger on image than on chemistry.  A
good clear explanation of the NiCad "memory effect" can be found in
Maxim Engineering Journal No. 25 (Jan 1997).

The second is that the rechargeable alkalines from Canada (sold in UK
under the trade name "Pure Energy") are remarkably good, giving long
life under "float charge" conditions. Unfortunately this company has
adopted a very low profile - in other words it's hard to buy the
batteries.

Overall, he finds that rechargeable Lithium cells (from Sanyo) have
fewer disadvatages than any other type, although the price is still
high.

In the past I've been responsible for buying and fitting tens of
thouands of Lithium primary cells. We found that some brands were better
than others. We had little poems about them:

A canny o-ld man
would always use Sanyo.

You'd have to be daft
to reject Saft.

But Varta defeated us. And then there's Tadiran, Renata, Sonneschein...

John Blackburn,
South London UK.