What kind of battery can power a 40 watt light bulb?

If the bulb is a 40 watt, 120v bulb, you would need 20 6 volt batteries wired in series, or 80 (!) 1.5 volt batteries. 1.5 volt batteries are AAA, AA, C, D, etc. Since this solution is rather extravagant, try finding a light bulb made for an RV. These typically run off of 12 volts, and you can get a single 12 volt battery, or 2 6 volt batteries, to run this bulb.