LTH 130 electrical problem

Hi ....I have a LTH 130 that I'm in the process of getting to run. The mower is in good condition, but after a few minutes running it will not power up even the slightest incline. I have been told that this may be due to the hydrostatic pump, or even just a change of hydraulic oil would solve the problem. Curious to find out what you guys think? Also, the battery currently shows a charge of 13.6V, but when the key is turned the voltmeter on the dash does not move, and the motor does not turn over...not even a click. Any one that can give me some troubleshooting tips would be greatly appreciated.
Thanks