When I plug my APM 2.8 to pc and plug the gps, APM recognizes it and it even gets locked. I can see gps lights flashing on top of APM. But when I disconnect apm from pc and plug it with battery, it doesn't work. There is no gps lights (it should be like a police car but its solid red always) on top of apm. I even tried to fly and switched to loiter mode but that didn't work either, it's same as stabilize, in loiter mode. What should I do now? Do I need power module or something different, like telemetry?