Forget the power. Keep the blade sharp and you will be happy.
Harbor freight has a power sharpener for about $30. remove the blade and it does a nice quick job of sharpening.
18 volt drills will work with 12 or 24 volts!. I 'wired' a dead 18v battery with 6 feet of 14ga extension wire. Female clips on the other end. I have a 30 cal ammo can which holds 2 - 12v small lead batteries. The 12v charger fits in the can. I carry the can and almost all jobs can be handled...