I measured a little bit more.

The lagging starts when the battery is at the voltage 3.4v and the "low" pin of the safe Shutdown Switch is at 1.6v.

Does anybody have an idea?

Hi, thanks for your reply. I measured the voltages, the system voltage is 4.75v and the battery voltage 3.27v, i think the PI is unable to play the battery warning. I noticed if i then plug in a charger the system shuts down. If I use another sd card with a system which is not running the safe-power...

Hi, i got my Safe Shutdown Switch working this week.
If i move the switch to off the pi starts shutdown. But i got a problem if the battery is low, the whole system becomes laggy and nothing is running smooth. Even the shutdown takes minutes.
Has anyone ever had that before?