Is it possible to put a more powerful battery in my phone?

Actually you don't have to get the battery powered case to get a more powerful battery for your phone! I haven't checked for this particular model yet but I know you if you look on eBay for replacement batteries for cell phones they almost always offer a more powerful same size,for the phone. But honestly if it's shutting itself down at 25% then there maybe be more of an issue then just with the battery. Also check your settings thoroughly too before going through replacement! Just incase there's a power saving mode that's set to $@$*!& off at that percentage. Still seems like it would warn you tho! Good luck!