Scott Cawthon, the game's creator, left "debug" codes in the PC version, likely for testing purposes during development. While there isn't a direct "infinite power" keyboard shortcut, you can instantly skip to 6 AM, which effectively renders power usage irrelevant.
Surviving Five Nights: The Ultimate Guide to the “Infinite Power” PC Mod (FNAF 1) fnaf 1 infinite power pc
If you don't want to sweat through 4/20 mode, you can enable it manually in your game files. This works for the Steam and original PC versions. Scott Cawthon, the game's creator, left "debug" codes
There is a semi-legitimate glitch in the vanilla PC version that grants almost infinite power. It is not a true infinite hack, but it allows you to survive Night 5 with 50%+ battery remaining. This works for the Steam and original PC versions
You can unlock an official (which includes Infinite Power and a Radar Map) by completing the 4/20 Mode (Custom Night with all animatronics set to 20).