Energy density isn't the issue. Need to either buy the best cells or oversize the pack to meet normal loads. Both options cost additional money.
Go look at the spec sheets on the cheap ones, they aren't power dense enough to make a small (1000-1500VA) UPS with comparable or even double runtime of the lead acid.
> about the same energy density per cubic meter
Energy density isn't the issue. Need to either buy the best cells or oversize the pack to meet normal loads. Both options cost additional money.
Go look at the spec sheets on the cheap ones, they aren't power dense enough to make a small (1000-1500VA) UPS with comparable or even double runtime of the lead acid.