Bushy

Electricity can heat as well as power devices. It can even be used to heat
the batteries, but if they were mounted on an extension wire in an inner
layer pocket, they can be kept at body temperature readily. It's an old
winter photographers trick.

Depending on the outside temperature is the size of the battery that you
have to carry to be able to add a resistor, say under a perspex cover next,
to provide enough warmth to get the display to it's operating temperature.

However, for weight and balance, and the big heavy jacket he'd be wearing,
he may not have been able to fly and achieve range.

Peter