When I installed my solar I was getting about 3,500 usable watts when fully charged before the inverter would show 10.5 volts, time to shut down. Now, 6 years later, I tested it today and I got 1,500 watts before hitting 10.5. These are VMax SLR AGM 155ah batteries. The system has be on daily all this time and up until this year tested fine. Your thoughts and help would be appreciated.