There is an indexing service that searches through your files and indexes the contents.
On initial startup, this can take a while and really eats into the battery. Once it's complete it should be OK though.
Unless it has found a corrupt file, then it just keeps running and draining the battery. If it has an SD card, then try removing it and see if the problem goes away. If it does then you might have a bad file and need to format the SD card.