What is a good auto feeder?

My cat is overweight and I was thinking an auto-feeder would help. I want something that will dispense a small amount of food 3 or 4 times per day.

Any recommendations? Are there features that I should definitely look for or avoid? I was thinking one that runs on batteries might be good in case of power outage (if I'm not home), but then I have to make sure I change them in time.