bestjetpilot

1st time with a prob. i have xs750 1979 and when i go for a drive after about 45mins the battery has discharged although the byke continues to work ok if i switch the byke off there is not enough battery to restart the byke. i have checkedacross the battery terminals with the byke running and there is 14.5 volts going into the battery which suggests the alternator and rectifier are ok. i kept a volt meter connected on another run and there was always 14.4volts approx going into the battery however the battery still ran down. has anyone any ideas what might be wrong.