Hey there my friend, nice game you have over here! :)
As others said, it would be nice to have some visual/sound feedback when you move over the batteries and when you are charging it (not showing the charge but that you are in fact charging it) to make it more responsive, adding a chill relaxing background music would make this simple game an award winning one for sure!
Think about it, aside from sounds and visual feedback, replace the bateries for common house items like: cellphone, ipad, speakers, tablet, smartwatch, anything you can find on your home! ;)
Keep the good job and thank you for your great game!! c: