The Sileno can mow your lawn in the rain and is suitably equipped for the task. Damage isn’t likely to occur during a typical rainfall, but power consumption is going to go way up.
Gardena and Husqvarna’s mowers both operate using a density sensor, which accounts for changes in the overall coverage of grass in a given area. Rainfall makes the grass appear dense so the mowers will operate at higher power outputs, and as such will consume more battery power.
They’ll still charge and mow the lawn, but it will take considerably more time than waiting for the weather to abate.