Need thoughts on battery operated sawsall

Anybody here have a battery operated sawsall. I would like to have one for junkyarding. Specifically for cutting off sheetmetal parts. I know the Li ion battery ones are the bomb. Any one out there that runs the longest? Has the most power etc? I know Li ion batteries recharge quickly and pack a big punch in power for their size

I was also thinking of getting a 12v to 110 inverter i can alligator clip to my trucks battery, or to a spare battery to recharge the batteries for the saw. However do they make 12v battery chargers for these tools?