If you have 4 12 Volt, 510 Ah batteries in parallel, it gives you a bank of 12 Volt, 2040 Ah.
The same 4 batteries in series/parallel to make a 24 Volt bank, gives you 1020 Ah at 24 Volt.
The total available energy will be the same; around 24 kWh...
If the batteries are in a cold place, do make sure that the charger temperature compensates... And if they are seldom cycled, try to run an equalize now and then...