There is something you have to drag infront of the battery. It should be noticeable when you activate it.
In future versions I'll totally include some tutorials xD
Aha, I found it! And now that I look back, it did stand out a bit from the background, which signals that it can be activated. Maybe make it stand out a bit more? Or make something you can interact with to get hints if you need to?
Thanks again for the lovely game!