Yeah, I thought about these things but didn't want to go into them. My Li-ion battery has an energy density 1/6th of TNT (4 MJ/kg) (but then a candy bar has even more, but you can't release it quickly.) The SLA battery is of course much less (it weighs 4 times as much). The weight issue depends on how much they save on the battery.

The caustic isn't a problem with SLAs. They will let SLAs on board, but not spillable ones. They are often found in power chairs, medical equipment etc.