* If the voltage at the battery is 14.5 volts while the motor is running then replace the battery.
* Make sure that the 14.5 volts does not go away.
* I assume you jump start the mower? or charge it?
* After you charge the battery and before you start the mower, what is the voltage accross the battery? If it's not in the 12 volt area, replace the batery.
* Good luck... Adios... Jasper