I posted this before but it doesn't keep the battery warm enough for driving temps. It keeps it at optimal temps for storage. That section of the manual I posted was from the section named "Storage." Just trying to inform.
Let me make some clarifying comments about how the car decides to warm the battery...
When plugged in, the car does not CONSTANTLY maintain the battery temperature BUT when the SOC drops below the re-charging threshold, it WILL warm the battery before/concurrently with charging if it determines the battery is too cold to charge safely. So yes the car will maintain battery temperature while plugged in, but only during a charge/top off cycle.
The following is based on older and unconfirmed info... Theoretically, and I say this because I just haven't seen a confirmation, the car will actively warm the battery if the battery gets below -7C(this comes from the SMT app).
The electrolyte in the battery cells is indeed a semi-liquid, and can indeed freeze. When it does so, bad things can happen in the battery.
As a result, Tesla will occasionally run the heater in bitter cold conditions to keep the battery temperature above the level where cold damage can occur - this is likely well below the temperature that water freezes.
Keep it plugged in. The amount of power it’ll take to do that is pretty small, and vastly cheaper than replacing a battery.