First attempt - fail. So much for theory
VCDS oil temperature at start: 11C
VCDS oil temperature after 20minutes: 11C
It was the battery's fault anyway. 12V 7.2Ah Aino Micro could not even supply 8A without its voltage collapsing to around 6V after only 10 minutes. I left it connected for just over 20 minutes anyway. Current dropped to below 6A, so that's around 36W input. After load was removed it recovered back to 12.3V
Next time I will try a proper starter battery with more capacity.