Wakelocks can definitely eat battery. They keep the processor running, and depending on the level of the lock will keep the screen on until the lock is released, and by your description it sounds like your trying to keep the screen on. The power button will still put the device to normal sleep mode unless you use a partial lock, but otherwise cannot go to sleep.
If you need to keep the screen on for some period or to subvert the normal sleep mode use a wakelock, but release it as soon as possible.
If you haven't already be sure to read the power management reference PowerManager | Android Developers