Say I have a project car with a dead battery and I want to get it running. Can I use any other car battery? Or do they have to use the exact battery for that make and model?
Yes, you can use any other battery
12 volts of course
If it will not fit in the tray, a group 27 for instance, you can run jumper cables through the window and put the battery on the floormat
Just about anything works in a pinch