Help - my t3i is misbehaving. I bought it used and have never seen movie mode act right. I'll put a fresh battery in, take a few stills, switch to movie mode, it'll start to record and then the battery will act like it's dying. The video will be interrupted. If I'm persistent, sometimes I can get a few minutes recorded but always with the death of the battery pending. Is there something I could do with firmware or maybe install magic lantern that would help? Is it possibly a weird setting conflict?
Have you tried using a different battery? If you've been using the same one for years they eventually lose their ability to hold a charge. so they may say full, but will be dead within minutes. Batteries don't have an infinite shelf life.
You can also check to verify you're on the latest firmware for your t3i. Look at the Canon website for that information.