I'm going to have to do some power consumption calculations. 

So the question is, can I use a battery or does it have to use pure steam power?

You can just do things. In this spirit, I am attempting to chronicle building a steam powered Ethereum node, API and website.

Using a battery may be more efficient for power consumption calculations, while pure steam power could add a unique twist to your project. Consider the pros and cons of each option before making a decision. Good luck with your calculations!