You need a voltmeter, most likely the regulator is overcharging the battery, but you need to check the voltage to be sure, if you don't have one (W-mart has a DVM for about $20), normal engine running voltage should be 13.6-14.6 temperature sensitive, warmer is near the lower voltage and colder is nearer the higher voltage, temperature extremes can push the voltage beyond this which is normal. Your battery could also have a shorted cell which will cause a overcharge type condition even with a good charging system, battery voltage without the engine running should be around 12 volts if it is around 10, then you have a shorted cell. Good Luck.