.. The first thing the battery needs

Fair enough. The game doesn't actually tell you what you need until you have all of the pieces, so let me give you a few nudges.

The first thing you'll need is a cable.

Some of the base's rooms are more technology-focused than others - they'd be a good place to look.

We know of at least one room where cables can be dubious - that might be a good place to check.

Directly opposite the computer in the computer room, you can find a cable ripe for the taking.

Next up - something made of copper.