I recall when they first came out they were six volts and had no power at all. My first tool had 9 volts, and did a fair job, until one day when the battery literally exploded when I was drilling into a piece of angle iron. My next was a 12 volt, and I used that one for years, and it had decent power. Finally the batteries died and cost more than a new tool. I bought an 18volt drill and it had no power at all, the 12volt one had been far superior. I returned the 18v drill and bought a 24 volt one which I still have, and it works quite well, except it seems the battery life is short, and needs to be charged far too often. Now I see they have some 36volt tools. When will this end? Will they keep raising the voltage for infinity? Why dont they just make a 120volt tool, which can be used on both battery and as a plug in, and be done with it. I never understood why they did not make ALL these tools so they could also run on AC while being charged. Just use the charger as the power source while charging the battery too. If there's anything I hate, it's when the daylight is getting short, and my battery goes dead, when I only have a few more screws to put in. Most of the time there's an outlet nearby, but instead I have to get out my corded drill, drag out extension cords, and put in the bit. A lot of hassle when they could have just made the cordless tool ALSO corded.
These days, I normally just use a corded tool if there is AC power nearby. That eliminates a lot of stress and annoyances. I only use the cordless tools when there is no power. Yea, I know someone will say that I need two or more batteries. Well, my old 12 volt one had 2 batteries and that was a definite improvement, but still it took longer to charge them than it took to wear down the "spare" battery. On my present 24volt tool, a spare battery costs more than I paid for the tool itself, so I just fight with the ONE battery and cus a lot. The F-Word has become my best friend whenever I use a cordless tool....