The manual is not clear. Page 194 talks about the start and stop of preconditioning and mentions only the cabin.I thought the manual 30min pre-condition just did the cabin temp and not the batteries
Page 348 has the following reference.
For the car to function, the high voltage battery and associated electric drive systems must be at the correct operating temperature. Battery capacity may be reduced considerably if the batteries are too cold or too hot. By means of preconditioning, using the charging cable connected to the mains power circuit, the car's drive system and passenger compartment are prepared prior to departure, so that both wear and energy requirements while driving are reduced. The high voltage battery that drives the electric motors is charged via a charging cable but can also be charged by means of smooth braking.
This is the only reference I could see. With all the other inaccuracies in the documentation, it is anyone guess as to what preconditioning does.