It'd be nice, sure. But regular deep cycles is precisely what lead-acid is not good at. Having said that, LiIon isn't that good at surviving deep discharge eith

It'd be nice, sure. But regular deep cycles is precisely what lead-acid is not good at. Having said that, LiIon isn't that good at surviving deep discharge either, although it is better than lead-acid. A battery management system can be used on both, which will turn off the power when there's still some juice left, to protect the battery, but people only ever seem to attach these to LiIon batteries.