Interval video and battery life

I've tried my hand at interval shooting and turned off the power save button to stop hibernation. I have set the interval to 30 secs (video mode)but after about an hour the battery is depleted. Got through two batteries now. The LCD screen turns off in between frames. Seems a low number of shots (120 ish) to drain the battery. Over a period of time I think I get a lot more than that in normal shooting.
Anyone else found that.
Dave