"Gareth" wrote in message
o.uk...

On 04/12/2010 23:50, Steve wrote:
"Gareth" wrote in message
o.uk...

On 04/12/2010 20:35, Steve wrote:
We have a solar powered alarm clock which automatically synchronises
with
the terrestrial time signal. The clock is marked 'PRECISION', 'SOLAR
POWER' and 'RADIO CONTROLLED'.

The display became faint and eventually it stopped working. I took a
look
inside. There was an unmarked AA size battery (leaking blue liquid
which
I
cleaned up). I measured the battery's voltage which was 1.6V, well
above
that of a normal rechargeable (1.2V?).


Was that with it in circuit of after you removed it? If it was in
circuit and being charged when you measured it then 1.6v may be correct
for a normal AA rechargeable battery.

Lithium ion batteries are around 3V when discharged and 4.2V when fully
charged. The 14500 lithium ion cells are AA sized (14500 = 14mm
diameter and 50mm long). However, beware that lithium ion cells can
burst in to flames if incorrectly charged so you want to be sure it
should be lithium ion before fitting one. If you do fit one, I would
recommend that you buy a battery with the protection module built in.

These came up after a quick Google:

http://www.ecrater.co.uk/p/9751735/t...ttery-900mah-2

http://ant-supplies.co.uk/Rechargabl...teries14500tf1

http://www.ledfiretorches.co.uk/batt...batteries.html

Thanks Gareth. The 1.6V was with the battery removed. The Li-ion ones
you
identify look interesting; you may have hit the nail on the head. As I
said to Graham (previous post) I may try connecting a couple of normal
AAs
in series to check if 3V does the job. If so, a Li-ion should work well.

As I said, you do need to be sure that your clock was designed to work
with a lithium ion cell as they can burst into flames if incorrectly
charged. If you do try it, make sure you get cells with built in
protection modules and don't blame me if your house burns down.

Gareth.
Thanks Gareth. Noted!!!