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.

--
Cheers
Dave.