70 hp Yamaha 1987 not charging

[kentrx1]

My engine quit charging this past weekend. My depth finder shows batter charging and suddenly it was not showing water depth and voltage dropped down to battery voltage (12.6) instead of the 16 plus volts it usually shows. After tracing wiring I discovered battery terminal bolt from battery was actually loose inside battery. I replaced battery but still not charging. Engine still runs and I know rectifier is an option and I have read service manual on checking it out but I am wondering if anything else could be damaged