A little feedback:
I didn't really notice the "fancy battery" change. Maybe it should be a more visible change.
I think if you change the "golden background" to some other material and then gave a watt bonus (something conducting better than gold).
Maybe there could be background upgrade selection which would give a bonus according to tier.
you could also put in a upgrade section where you can buy extra batteries.
I found one bug. I can't mute the music. When I go to the settings menu i can mute it, but as soon I press back the music comes back up.
With all that said it's still a good game. Well done...