SD card issue RP1

I've been using the SD card as internal storage. I've noticed over the last couple of days that the battery is draining real quick. The last time I had this issue the SD card was corrupted and re-formatting it fixed the problem so when I checked the SD card this morning I wasn't too surprised to see it corrupted again. Anyway the issue I have is that I cannot now format it as internal storage. It gets to 40% then goes back to the storage screen and says checking card, which eventually says corrupted again. Formatting it as removable works fine but is of no use to me. I don't think it's the card as when used as removable I can move files back and forth without issue. Any ideas please?