JD 180 Regulator Voltage

[bobsphotos]

Can someone tell me what I should have for a charging voltage when my JD 180 lawn tractor is running. I cannot determine if the battery is bad or if it is not getting a high enough charge voltage. Any help will be appreciated.

 

[t man]

Normally charging voltage is between 13.5 - 14 volts. at operating rpm.