As 45,000 properties across Sydney's eastern suburbs went without power at the peak of the city's heatwave on Thursday, one homeowner was the envy of his neighbours.

Thanks to a home battery, Carl Prins was able to keep cool, watch TV and take care of his week-old baby daughter while his street in Waverley was blacked out.

Carl Prins' Telsa battery helped him keep the lights on during the eastern suburbs blackout. Credit:Kate Geraghty

"We would have had to get in the car and go to Westfield [shopping centre] or the library to stay cool," Mr Prins, 38, said.

The Powerwall 2 produced by tech billionaire Elon Musk's Tesla company is meant to detect grid outages and kick in automatically, but Mr Prins was surprised it worked so well.