We have two Tesla batteries in our Bell 214ST, and it cranks fine in -30°C temps (and colder). The batteries are self charging and self heating. We plug in an extensioncord and that is all that's needed. We have a separate Herman Nelson heater that we use to heat up the elastomerics of the running-gear.
I have flown Tesla batteries in Bell 206B and L3 helicopters, and the starts were incredibly fast and cool in both. Down to 11 seconds from introducing fuel to 58% on the Jet Ranger!
Anyway, fantastic batteries!