The final cut of TMC Podcast #21 is available now. We covered the recent wide release of FSD Beta and shared our experiences. We also discussed the best times to charge and Tesla's official CCS adapter. You can watch it on YouTube.
Well the theory is that initiating the climate control also initiates any battery warming, so you could just use the app to turn on the climate control to the current cabin temp. That way the car isn't really doing much heating/cooling for the cabin but if it decides it needs to warm the battery, it will.
I haven't done an experiment for it, but I have noticed that the regen dots show up more easily the higher the battery charge % is (not surprisingly - even the supercharger tapers significantly, well before full charge, and I think that max regen on the Model 3 is > 60kW (my Spark EV maxes at 60kW and it is a much lighter car and the regen is not quite as strong)). One of these days I'll measure the deceleration and calculate the power with the VBOX.
Anyway, I think it's probably a combination of charge state & temperature. You'll probably have more limited regen at 40 degrees when your battery is at 90%, vs. when it is at 30%. But that's the "experiment" I haven't done. And I think if you're at 90% you may have a hard time getting rid of all the regen dots.
To pre-heat, yes, the claim is that preheating the cabin will do this, but there is not direct control AFAIK. But not much point if you're not plugged in, and even if you are plugged in, it's unlikely to be a net energy benefit to you. (You're unlikely to recapture enough energy through higher regen to offset the additional energy you use to warm the pack & the cabin - whether it's coming from the wall or the battery itself. So you're not saving the world by warming the pack to get better regen. )