Although there is the possibility that the charging regulator system has developed a defect which will obviously require repair, but first of all I would advise you to try discharging the battery with a small 6.5 volt torch bulb or similar until there is just about a very dim glow from the bulb then try another charging test. If however it still does the same then that could indicate with about a 90% certainty (still possibility of battery fault!) that its the regulation system.