Sadly, I was not able to find any useful repair guides for you specific camera. Though, I was able to find some parts that might be able to fix the camera. These are off of ebay, so your purchases are at your own discretion.
Here is an AC DC input door that I found for the camera.
GENUINE FUJIFILM FINEPIX S700 AV DC IN DOOR REPAIR PARTS
Here is a battery holder tray that I found for another type of Fujifilm camera that might work.
If neither of those work you can contact Fujifilms for a warranty if you still have one. If your warranty expired, then you may need to just tape over the battery cover to keep it closed. Hopefully this works!