I too wonder about the very high voltages quoted for some tools. Anything over 48V or so is going to need a physically large pack.
My 10.8V (later re-branded to 12V) DeWalt tools just keep going, the impact-driver is particularly good. If you don't have an impact driver, get one, far better than using a drill to put in screws.
I will say you tend to get what you pay for, the weak point is almost always the batteries (which are of course unobtainium when you need replacements), and whilst it is possible to re-cell they never really work as well.
If your batteries really are still good, then getting a tool that uses the same ones is sensible, but not all packs that look the same are actually interchangeable ????