I'm tring to install a chain lock on the inside of my home. I've tried millions of things to get a hole in the steel door. Is a 12 volt drill not powerful enough?
As @DA01 mentioned, a good 12 volt drill should manage this just fine if you are using a drill bit designed for metal. I have had metal doors on my last three houses, and all were easy to drill.
If you are using a battery powered drill, it may have lower torque than a wired drill, but that wouldn't be a problem here - as long as the battery lasts until you are in:-)
Drill power is not critical - you just use a sharp drillbit suited for cutting steel and drill long enough periodically cooling the drillbit with water so that it doesn't burn.
I personally made about two hundred holes in shaped tube with 2-millimeters thick walls when assembling a fence. I used a rather weak looking professional Bosch GSR2 10,7 volts Li-Ion powered drill/driver - that's a good tool, but not a tool one would consider extremely powerful, I had to recharge after about each 30 holes and drilling was certainly slower than with a 500 watts mains-operated drill, yet it was quite doable.