I have a small Back-Ups 1000 RS unit. The red replace battery LED went off so I replaced the battery. Now it comes up but every few minutes it will beep 4 times and the replace battery LED flashes. Looked in manual and can't find anything on this beeping. I checked the connectors and I even let the battery discharge which it took almost 30 minutes with a load on it which tells me battery is pretty solid. Any thoughts?