Have been riding my Shocke, Bafang 8FUN and C961 screen, for years with no problems, and nothing visibly wrong now, but after 4 miles, it just shut down. Turned it back on, and a few seconds later, it shut down again. With a slight click sound. Over and over. Battery tests fully charged . This has happened several times for about a week now. Any tips on troubleshooting ?