Those things are all noob things that you learn with time, base is pretty nice and pretty solid!!
For the hitboxes, a general rulenis to make them sigly smaller than the sprite, except for good things; collectibles, coins, in your case the batteries, should be a bit bigger; if you die near something dangerous without touching it, it will feel unfair, and if you touch it just a little bit and don't die, it would be that bad. But if you try to reach a collectible, you touch it just a little bit but dont collect it, it will also feel unfair. It is a bit difficult at first do get how the things feel right or wrong, but youll get it with time. Just, test it, play your games, change what you feel like you dont like. I also recomend, when you feel like the game is alright, send it to a friend and make them test it, let them tell you how they feel playing it, since sometimes you will not be able to see if something is not working right and a new oppinion will help you.