LiPoly batteries should be kept warm for charging and flying. Some chargers will automatically only charge about 90% if the charger senses a temperature of 50F or less. Fully charged batteries need to be kept over 50F or will be over charged. Of course none of that is new information.  I had opportunity to fly at about 38 - 40F with wind 3-6 mph and sunny skies and wanted to keep the batteries up to temperature.  In the spring when the temperatures are still sub 50F I have used an insulated box with a reusable gel pack type warmer but decided to try for a bit more warming.

Some use fire boxes to store batteries for travel and home and those will keep batteries fairly warm if preheated, and with preheated batteries.  the Honeywell unit below has adequate mass to work for a couple hours or more.  I warmed it while opened in front of a fireplace for a couple hours.  Temperatures not measured, but it was still quite warm in a couple hours.

https://www.amazon.com/First-Alert-2017F-Water-Chest/dp/B000GB1VMO

Also tried was 12V warmer lipo bag.

https://hobbyking.com/en_us/turnigy-programmable-lipo-battery-warmer-bag-12v-dc.html

The bag is shown below with 4 packs of 6S TP 2700s.  With the top closed a bit longer and less sealed, 4 Zippy compacts also fit.  If pre-warmed the useable time from a 3S pack was still good after 3 hours.  

Whatever your solution is, it will be a lot easier than starting a real engine in the winter.

Have you tried lighter fluid?   It helps to get the one bump off the compression starts on those inverted mounted engines.  

The price of about $15 does not include the battery as you can see from the HobbyKing link.  I had an old 3S pack.  Also easy to run off of a car battery or in-car plug, or your choice 12V source.