Sorry, just found the time to respond. I checked the rootfs and saw USB/debug scripts (what I meant by debug mode) and a kernel console on ttyPA1, so I doubted they left no recovery path. Like you said, it's probably DFU over USB or an internal...
Mavic 2 Enterprise self-heating battery
Temperature Range: Self-heating can occur when the battery temperature is between -10°C and 6°C.
Charge Requirement: The battery must be above 50% charge to activate self-heating.
Manual Activation: Hold...