I had trouble, a while back with one of my lipo batteries. It was the bms box that went bad. You can get online and find out how to open the battery up and how to test the cells with a multi meter. The manufacture sent me a new one from China, but I got one delivered from Amazon the next day for $35. I am still running the Amazon bms, but I have the new up graded one from China sitting in the drawer, just in case.