Well, for me there were a couple of reasons:
1. Dead batteries suck! And, when you're running a circular saw, saw-zall, or pretty much anything else constantly, dead batteries happen very frequently.
2. Batteries are not cheap, and they don't charge fast. Even with 5 batteries and 3 chargers, a good-sized project + my questionable competence at most things one can do with power tools often leads to waiting for dead batteries to recharge.
3. More power:) You've overclocked your computer, so why not overclock your power tools?
4. I *think* this'll be a bit more energy-efficient than recharging and discharging batteries... certainly more earth-friendly if you take into account impact of metal used in extra batteries you won't have to buy...
As usual, this is not the safest or most professional of projects. Please don't hurt yourself any more than you'd like to:-)
Here's a video:
Step 1: Gather Your Supplies
-cordless tool(s) to make work corded, complete with charger. I used these.
-an old ac power cord that you don't mind ruining
-an extension cord to run between charger and tool
-foam or something else that's nonconductive, flexible, and easy to work with. i used a dried-out piece of the nastiness that is known as great stuff.
-your favorite roll of duct tape
-aluminum foil or other conductive, flexible material
And, it'd make life easier to have:
-something to make the corded adaptor easy to remove from the tool. I used these, and they worked well.
-pocket knife, leatherman, or other way of cutting and turning screws
-a pack of spare batteries, like these.
I'm sure you can do this with other tools; I happened to have a set of the cheap-but-usable Ryobi stuff, so that's what I went with.