500 watt-hours is 62.5 amp-hours, assuming the voltage is 8 volts (V).
Determining the amp hours from watt hours is reasonably straightforward, especially if you know the voltage. You may use the formula:
Charge = Energy / Voltage
So, you figure out the amp hours, which is the unit of charge, by dividing the watt hours, the energy, by the voltage. Read more