Portable battery jump starting. Hook ups and 12 or 24 volt

With the coolant heater get the timer and set it to start 2 hours before you want to start the engine. You can start after 90 min heater time down to -30F.
The air-heater uses much less power per hour but you will need to charge your batteries after 10 hours run time at -5F or you will need a boost.
This goes for modern Webasto and Espar heaters with the exception if the Webasto 2010which is a coolant based heater that has 2 to 3 times more btu than modern systems.

 

It is a coolant heating chinesium grade "hcalory"

We shall see what happens, in the meantime, ill have the booster with me