On Oct 9, 8:21*pm, "Dave Plowman (News)" wrote:
In article ,
* *Andrew Gabriel wrote:

What would be _really_ nice is if they had a switch setting
to automatically start charging when mains is applied. That
could be the basis for an effective automatic emergency supply.
Sadly, they don't do this.

Yes. Wonder how easy it would be to modify?

--
*Save a tree, eat a beaver*

* * Dave Plowman * * * * * * * * London SW
* * * * * * * * * To e-mail, change noise into sound.

Here are some numbers recalled from working days.
When one typically dealt with 24 cell, nominal 48 volt, large capacity
telecomm. batteries and occasionally with other varieties/sizes!

Voltages per cell and for a six cell car battery.
Charging voltage; 2.3 to 2.4 volts/13.8 to 14.4 volts.
Floating/trickle charge to keep batteries alive and fully ready for
service, 2.15 (British Post Office) to 2.17 (US. ATT&T etc.) 12.9 to
13.0. Just a few milliamps going to battery bank to offset natural
self discharge tendency. A non trickled battery in good condition can
self discharge in several months.
In other words any 14.5 volts and over can boil a wet battery dry.
A trickle voltage below say 12.5 not much use.

Another yard stick read somewhere was; after some 12 to 24 hours after
being fully charged (not over-charged) a battery in good condition
should settle down and assume a nominal voltage of around 11.8 to 12
volts.
If it's anything below that or down to say 10.7 volts or below,
battery is shot! Haven't tried that myself, although got several old
truck batteries that were refreshed recently, so must try it!

PS. Forget nonsense about modern encased batteries discharging if
stored on a cool cement floor. Old wives tale due to earlier, probably
porous rubber encased batteries of an earlier era!

BTW Apropos the "Save a tree ................. " Try this: "Save fish,
hunt some seals". The 500 year old fishery off the east coast on
Canada/North America has been decimated by a) Overfishing and b) The
millions of seals who will eat almost anything marine!