a few notes: the batteries should be stored above 15 degrees Celsius. if you then fly in the cold it is not a problem. as paul said.
you should note if the battery has been stored cold for several days, for example.
at just plus 3 degrees Celsius. that it takes at least 12 hours until the battery is evenly warm again inside if you want to heat it above 15 degrees Celsius.
there is a lot of mass that has to be warmed up.
if the weather is very cold and the eppg is placed in a warm room after flying in minus degrees, condensation can form everywhere on all cold aluminum parts. also partly in the controller inside.
It is therefore better to adjust the EPPG to a mid-colder room first. as an example, let it stand in a garage for a few hours before taking it into the house. eppg generally love cold weather. you don’t have to let the engine warm up like with a gasoline engine