One CR2032 button cell (3V / 10 mH) Attention: the remote control transmitter can operate a maximum of 3 devices, the lower row is called ALL and switches all 3 upper devices on and off at the same time! It is therefore impossible to operate more than 3, and the frequency cannot be changed.
Thank you very much, Kangaroosky, for your precise answer. I always have CR2032 in stock, as I use them a lot, e.g. for my 2 remote car keys, blood glucose meter etc etc. For the remote control of my old socket remote control, I always needed the small 12-volt batteries (23A), which are not available everywhere and are considerably more expensive.