It's likely that the screen is just dirty. Try cleaning it with a microfiber cloth (like the kind you would use on a pair of glasses). If that doesn't work, there may be crumbs or other messes stuck in the edges of the screen (this can be enough to throw off the screen's calibration). If you see any messes in the cracks around the screen, try gently removing them with a toothpick or a spudger. If that doesn't work, you may be dealing with a larger issue like a damaged screen or a loose connection. If you think this may be the case, take a look at the LeapPad Platinum's troubleshooting guide to help you diagnose your problem and find the right guides to replace any damaged parts.

I'm assuming you want to replace the battery because you are having issues with battery life or because your LeapPad won't turn on. May I suggest checking out the troubleshooting page to rule out a simpler solution before you tear your device apart? The battery is kind of a pain to replace so I want to help you avoid that if I can! If you determine the battery does indeed need to be replaced, it is possible to do so. My team and I will be writing a battery replacement guide very soon, so keep a look out for that!

The solution may be as simple as just randomly pressing the directional pad until it pops back into place (you can find more information about how to deal with messed up buttons here). If that doesn't work, unfortunately you'll have to open up the device and reposition the directional pad that way. You can access the d-pad by removing the speaker components from the device (follow the steps in the speaker replacement guide).