First find out what the power limit on the battery is (19kW/h doesn't tell me if that's the capacity or power delivery. Usually it means the capacity))
Volt x Ampèere(max) = Watt/hour. (deduct at least 10% of that)
Do you even get 500Watt?
Do you need a step-up / step-down to deliver the right amount of Volt to the PSU?
If so, buy or build one.