"tony sayer" wrote in message
...
In article o.uk, Dave
Liquorice scribeth thus
On Tue, 13 May 2014 04:54:43 +0100, Bill Wright wrote:

Given two 12V lead acid gell batteries, both new, both the same type,
but from different sources, how do I balance the charge before fitting
them in a 24V appliance?

How are you going to be charging them, series @ 24 V or
parallel/individually @ 12 V? Even if you start with exactly the same
charge in both it won't be long before one has more (or less)
capacity than the other. Series charging is likely to make things
worse.

Making sure that you never discharge below about 1.1 V/cell(*) will
help maintain balance but they won't stay in balance.

(*) Memory, have a google for the battery makes specs, you might be
able go down to 1 V/cell.


Interesting..

Over time I've been to transmitter and comms sites were they sometimes
have stack's of 2 volt cells around 500 odd amp hours each, but they
are just strung together to make 24 or 48 volts, so are they likely or
do they get one cell go "astray" and if so what can be done about it?..


*Astray meaning go wrong capacity wise in some way or 't other;!..

You do a periodical balance charge, which holds the batteries at a higher
than normal voltage for a time,
my motorhomes charger used to do this every 35 normal charging cycles, it
would take the battery bank* up to 15 and a bit volts for an hour or so,
causing them to gas vigorousely, part of the battery maintinence was to top
up the cells with distilled water every now and then, i didnt go as far as
adding the auto pumped watering system tho, as i found a check every 3
months was adequate,

*6 x 232 Ah 6 volt batteries in paralell and series to give me a 12volt 696
Ah battery bank.

BUT, that was for flooded vented cells, not sure what the equalizing voltage
for gell cells is, if there even is one,
As they are likely to be used in a granny chariot i guess, just charge them
both up to full on a 12 volt automatic charger, then connect them together
for your 24 volt bank, and charge as one battery from then on.... as that's
what the charger will see it as.... and it is just 12 x 2.2 volt cells in
series.