This was a 1/2" corded drill. No batteries. Battery power drills won't mix a full bucket of concrete. Well, they might, but they won't do it well.
Clean off the commutator, new brushes (or maybe just springs)... wait, what am I saying? They're pricing them so aggressively a new one is cheaper than a battery. What a waste.
LiIon > NiMH > NiCd
More volts = better
I have a couple of 18V Bosches that have served me well; I was torquing 3" screws through 2x4s a few weeks ago.