I've been flying my Mavic in temperatures down to about 0F with pre-warmed batteries and haven't had any issues, or noticed any warnings yet. I also hover for a minute or so after takeoff to help it warm up. I've noticed that with the Mavic turned on but engines off, it generates quite a bit of heat on the lower side, and I suspect it heats up even more with the engines running. I've also been keeping my cold-weather flights relatively slow, and I'd imagine that higher airspeeds would suck heat from the batteries much quicker (convection heat loss increases non-linearly with the airspeed). I wonder if a thin, light insulated cover velcro'd over the top of the battery might help. In fact, it'd be interesting to design a lightweight rigid wrap-around shell to channel the hot air underneath around and up over the battery, for use in cold weather.
Also found my limiting factor to be cold fingers. I just picked up a pair of North Face Canyonwall eTip gloves which seem to have pretty decent dexterity and work better on my touchscreen than anything else I've found so far. We'll see how well they work outside later today....