SRD will shift to green when the batteries get low. Sounds like the batteries need to be replaced. Here are instructions for replacing the batteries in our old hilts with plugs:
http://img23.imageshack.us/img23/6147/ultrasaberdiagram.jpgIf the saber doesn't have a plug, but instead has a rubbery pommel, then you can just slide the pommel off and get to the batteries that way.