Club car charging won't stop charging

Hi

I have a 2013 club car with batteries 18months old.my problem is it won't fully charge.When charging it gets to fully charged then the charger stops for about 2minutes,then starts up again.The golf cart seems to run fine.but the other night I left it on charge overnight and I actually forgot about it,then 18 hours later it was still charging.can anyone advise me why this is.it only started doing this a few weeks ago.before that it would always charge for 4 or 5 hours and charge perfectly then stop charging as it should….

Please help.