Hi Ted,
Welcome to audiocircle and the RWA forum!
How is it that the batteries both stay at an equal charge when charging? It seems to me that the batteries would become unbalanced if it is a 2x12v series system charged by 24v.
We use a battery analyzer to closely 'match' the two batteries (especially in terms of their internal impedance) so when they are charged in series, the voltage across them is approx. the same. Since they are in series, the current that flows through each battery is the same. So you want the internal impedances to be matched as closely as possible in order to get approx. the same voltage across each battery during the charging cycle.
I thought a 2x12v system had to be charged in parallel by a 12v charger to keep it balanced??
24V SLA chargers are designed to charge two 12V SLA batteries in series. They even make chargers designed for 36V and 48V (for 3 and 4 batteries in series). Again, the trick is to match up the batteries with an analyzer as mentioned above. IMO, with two batteries in series, it is very doable. If going with more batteires, I would charge them in parallel. But when charging in parallel, the batteries see equal voltage but will draw different amounts of current (again, matching the batteries tends to minimize this).
Hope this helps,
Vinnie