the batteries eventually go off in any rechargeable device

generally speaking, the higher the voltage the more power and life you will get from a charge

I use the Longacre 24V version that comes in a case with the charger and 2nd battery and keep a 12v-120V inverter in the tow vehicle in case a battery needs to be charged. Just replaced the last one I had for 6 or 7 years not because the batteries are dead but because the sun spur gears inside the head were finally worn out and started jamming. It was not too difficult to take it apart, unjam it, re-lube the gears, then reassemble it, but several months later it will do the same thing again. The latest version was on sale at Solo Performance and I had won a $100 certificate from them in a raffle, so between the sale with additional year-end discount and free shipping the new kit cost me $90.

they sell a cheapo 24V gun with single battery that has a decent reputation

Nieko Tools 24V Cordless Impact Wrench

these are more than suitable for the average wheel change etc., but for serious work (flywheel nut etc) you'll need a large electric or air powered gun

 

While changing out my exhaust system, I needed to take off the black brackets that would otherwise keep you from pulling the cat off. Even though I'm sure they are not torqued down much, my kobalt impact wrench was super convenient for getting these out. As far as how many hammers it takes to get lugs off, I guess it all depends. I have always torqued my lugs down pretty tight with a cross-bar. On my dad's accord which have not been taken off in a lonnngg time, and which I'm sure were last tightened with an air wrench, it took 5-6 hammers and then it'd spin right off.