I brought this very question up to the rep. when I was doing my cervical trial. He said they have to place the battery at a specific distance below the skin because if it's too deep then the charger that sits over it to charge it up will not work. They need to be able to "connect" in order for the charging to take place.

He did tell me a funny story. He said one "dude" that wears his pants down by his behind (you know who you are ) was complaining about the battery rubbing on his belt. Of course I would have said "pull your pants up", but they went ahead and moved his battery for him. So seems like they're pretty used to having to move batteries for various reasons.