The converter is an Inteli Power, model PD9245.
As for why I would only go for such small capacity batteries: The ones I have now is this size, and without modifications, I can't replace these with anything bigger. Then for the extra batteries, I thought you should try to keep the battery banks balanced, and that would mean using the same type.
Or could I use bigger type for the extra batteries?
If I'm going for something bigger, what would be the limit? Will not the converter eventually start struggling when the battery banks get very large?