Also see my Lithium battery page…

Increasing the domestic bank size can be a good idea as it can provide longer intervals between recharging.

New trays neatly welded in with batteries strapped down and terminals covered to comply with BSS standards.

Batteries can be balanced so charging currents and loads for each battery are even. It’s sometimes possible to increase the bank size using 6V Trojan, Crown or US Batteries: 4* 6V batteries will generally fit in the same tray as 3* 110AH.

Before thinking about increasing a domestic battery bank you should have means to properly monitor and manage the system with some sort of battery monitor. Also you must have means to recharge a large battery bank properly with suitable alternator.