I have a 14.4 volt 3/8 hammer drill. The 2.4 Ah batteries really won't do that much plus they are very expensive and at 14.4 volt even hard to find. My batteries are all worn out. I've wondered if I could run off the same sealed lead acid batteries I use to run all my survey gear (I have several sizes). I need to drill a few rocks for markers on a small mountain subdivision I'm doing. So I took apart one of the drill batteries, took out the guts and soldered up to the contacts so I could hook it up to a 12V battery. I tested it and it works fine (I had to get larger fuses). So now it's a cordless drill with a cord to a 12V battery. I have all the power (sealed lead acid batteries) I'm willing to pack in to a drill point.
I, too, have a corded cordless hammer drill, an old DeWalt that was really too small to drill holes in concrete reliably anyway. The batteries got hard to find and absurdly expensive, so I replaced it with a real rotohammer, but decided to keep it alive as a semi-cordless unit just because I didn't want to throw it away.
The bad news is that it has sat on a shelf for over 10 years now because I have more suitable tools available.
I don't really have a great need so the little drill will keep me going (I have five rocks to drill). If I do go to to real rotohammer I think I'll just get a normal corded and get an inverter so I can still operate from batteries in the wild when I need to.