Where weight and energy density is not a concern, you'd just use regular old-fashioned lead-acid. Lots of charge cycles, easily recycled, simple, no overheating, existing infrastructure.
When the Powerwall was announced, weren't people explaining one of the benefits over lead-acid based systems as you don't have to worry about accidentally generating noxious or explosive gases if the system isn't well vented? I just found something regarding that[1], but I'm unqualified to know how much of a problem this is in reality.
