Its sounds like its knackered my one went the same way.Go to Mapland and buy a 12amh one and get a smart charger just make sure the polarity is correct red with red wire and black wire with black. The smart charger might correct your old battery as may one did , its about 20 quid and the battery is 35 quid but it will last longer also fasten the battery down as they flop around and short out.