I've been playing with battery preconditioning over the past two weeks. I should be taking notes and should also wait until our next cold snap (likely next winter), but I've observed the following on modestly cool nights (~40° ambient):
PC ON, I find my battery pretty consistently at 19°C (66°F) at night, leaving work, at the end of an 8 hour charge session on L1 (16 amps). Mid-state charge level 50%-80% usually, never at 100%,
PC ON, I did the same experiment on a 32A L2 charger at work, an found the battery again at 19°C.
PC ON, pre-charged to 100% (so little if any residual heat from charging), plugged in to L2, and the battery reported 16°C (61° F).
PC On, pre-charged to 100%, plugged in to L1, now the battery is at 10°C (50°F).
PC Off, charging L1, I consistently see 19°C.
PC Off, no charge (unplugged), I haven't been able to get good readings since my ambient temps have been too high -- I need some mid-30° F days where I can count on little latent heat being left in my battery.
10°C sounds like a low temperature for a battery to be pre-heated to, but as a basis for comparison, I also own an ID.4 that heats the battery only to 8°C (46°F), and allows it to warm "naturally" from that point onward through internal resistance during discharge/use.