DJI Drone Battery Heater and MOSFET Upgrade

In this video I demonstrate a home built battery heater for my two DJI drones. Both drones use LiPo batteries and when flying in the winter with air temps down near or below freezing you need to keep the batteries warm to permit safe flight. There is smarts built into the firmware of the drones to inhibit flight or reduce performance if the batteries are too cold, but it's better to avoid that problem by heating the batteries before use. The heater I made is a re-purposed cooler that I've added a heating element, a temp controller, and a buck converter power supply so that the unit can operate inside from AC mains using a re-purposed laptop power supply outputting 19VDC or outside in a car using the cigarette lighter port from 12VDC. I can also run the heater from any of my drone batteries as the buck converter is good to 30VDC -- well above the highest voltage any of my batteries output. The temp controller used was a $9 item I purchased from Amazon. It is an ON/OFF controller (not PWM or PID) that uses a thermistor for temp reading and a relay to control the power of the heating element. The second half of this video details the modification of the temp control board to replace the relay with a P-channel MOSFET. Using a MOSFET will eliminate the failure modes of burnt contact or mechanical failure that can happen with relays -- the MOSFET can switch millions or billions of times without failing. Yes, the heater is a bit crude looking as I bonded the PS and temp controller to the lid using epoxy and silicone sealant. This unit isn't well suited to being left out in the rain, but my intention is to leave it in the car anyway so that shouldn't be a problem.