battery won't charge?

I have a Napco P800 and the battery will not charge while connected to the system. I have purchased 2 new batteries thinking it was the battery itself and finally I decided to disconnect the battery and use an outside battery charger to charge the battery. The battery itself charges fine and will work until it loses it's charge because the alarm system is not charging it like it should. Is the panel bad, or is there something else I need to look at as the culprit? I also found 2 plugs that seem to have something to do with the alarm system. Does anyone know what TWO different electrical plugs are needed for?