thx! any way I can fix it?
Try lightly dampening a magic eraser, just enough to gently buff out any staining, don't drench it or you risk getting the vpet wet. Then, invest in a case to protect it from future staining. There's silicone and hard plastic one's out there from reputable etsy sellers you can try. Opt for a lighter color, they'll be less likely to stain your device going forward. Also be extra careful where you've buffed out the stains afterwards. Magic erasers are essentially a very very VERY fine sandpaper, meaning the buffed up spots would be more likely to hang onto dirt and grime going forward(hence my reccomendation to buy a quality case).
That said, if you're worried about it being a battery issue, open it up and take them out! If the batteries are leaking, it'll prevent further damage. It's generally bad practice to leave batteries in a device when you're not using it anyway. If you're not gonna play with it for a week or more, remove them. If there has been any battery leak, there's guides on how to clean that up- thankfully I've never had to deal with that, but it also means I don't have any advice on how to fix it.
Also, define way too quickly? Have you looked up the average battery life of the remakes? Is it on par with the average? If so, there's not too much you can do.
If not, however, what brands of batteries are you using in your remake? When were they set to expire?(expiration dates are noted on battery packages for even dollar store ones!) If you're using the 2 for $1USD dollar tree that are a week from expiration batteries, you're simply unlikely to get a lot of battery life out of them. I have bought a pack to test on some devices and get a feel for their lifespans firsthand, but even so, I expect far less from them than a $6 energizer battery from the drug store set to expire five years from the date of purchase.