Lead acid and AGM batteries have essentially the same cell voltage so there
won't be any catastophic type problems from hooking them in parallel.

The internal resistance of any two batteries can vary, even different sizes
of the same type of battery. This can lead to uneven charge/discharge
characteristics between two different size batteries hooked in parallel.

There is one situation where connecting AGM and lead acid together could be
a problem: many "smart" multi-cycle battery chargers have an optional
"equalizing" phase. This mode intentionally charges the battery above the
"gassing" point in an attempt to burn off sulphates on the plates, and thus
restore lost capacity. You don't want to do this to a lead acid battery too
often, but you NEVER want to do it to an AGM battery.

On my Heart Inverter this mode requires manual operation to start. Just make
sure that the AGM batteries are disconnected when (if) you this and you
shouldn't hurt them.



Rod