Acer M5-581T Won't boot off Battery but it works

I have a Acer M5-581T ultrabook that works fine but won't boot off the battery. The battery works ok is seen by windows and the compuer. I have to plug in the AC power cord and turn it on, as soon as the lights come on i can unplug it and it works for hours off the battery. but i cannot boot it without the AC plugged in.