It really does depend on what was the Temperature setting & where the fridge was (ambient temperature) . If the fridge is set at 3 deg - it wont work much at all .
I just checked my EvaKool in the Canopy - There has been no charge added since around 7pm & at a minus 2 deg setting ... over 14.5 hours the battery is at 88% ( 100amp LiFePO4) - that's about 0.8 amps / hr overnight
so the power draw can actually be pretty low
Chris