It's not uncommon after battery replacement on these to have some weird behavior if some of the pins on the battery connector were damaged. But since that requires dismantling the whole device again to check, it would probably be easier to have a look to see if there are any panic logs that come with this. Have a look at the [[iPhone Kernel Panics|iPhone Kernel Panics|new_window=true]] page. This will also apply in large part for iPad.
Feel free to post the panic if you find any.