We have solar and powerwalls in southern NH. We also have ground source heatpums which are efficient but use more power. Powerwalls charged itself to 100% on thursday night and went on standby. Lost power at around 6:18 am on Friday morning. Did not notice a thing until I saw a notification from tesla saying powerwall is 95% charged and providing power to your house. We turned down the heat and flipped the propane fireplace on. Switched the heating to emergency propane heat but fireplace was able to keep the house warm. Other than heat pumps we did not make any changes to the power usgae and by the time power came back at around 4 pm we still have 90% battery capcity left (total 26 kWh). Even with the rain and cloudy weather we had roughly 3 kWh solar production to offset some of the electricty usage during the day. If we would not have got the power back we would have lasted at least 24 hours with propane fireplace and propane furnace.

This was the longest we were without power and really appreciated the battery backup we had.