@mitu I can confirm: downgrading SDL to v2.0.8 solved my problem! Thanks for the help, as always. :-)

Any update to this? I hate not knowing how much battery life is in my controller.

After hearing the replies I think I will just power it on with the front button. Thanks for the replies!

@mitu Ok, just tried that. Controller disconnected on 3rd lap in Cortex Castle time trial. I executed the command through SSH while the board was connected via wifi (duh), but then I was unable to connect again and checked in Retropie wifi settings and there was no info of any connection, so I guess the command worked. But it apparently didn't help with the problem...

@AnotherLife I added some information about that topic into RetroPie docs a few days ago