I changed my battery three months ago got a new Excide one from car parts for less (more amp hours than standard unit) been fine until two days ago when it went flat. When my cars is at idle or above the amp/volt meter is showing above 14 volts so alternator must be fine. Took out the battery & Put it on charge for 17 hours and still the indicator dot on the battery has not gone back to green. Does this mean I was sold a dud battery. Any ideas?