When you do try those high capacity batteries, keep a close eye on the max watts. Just in case.
But, from the sounds of your 24V 18Ah test, it seems like the inverter is self-limiting.
As I think about it, it seems only logical to have the controller chip programmed with
power limits, to prevent things from getting too hot on those occasional
perfect solar days..
I'm still thinking about getting some of those thin-film panels (54V~2A),
Kaneka Thin Film Solar Panel 110w
The price looks good, if they ship them by
Ground.