thx for your fast reply. i'm in the train right now. so i can't provide you now with any pics. as soon as possible i will do that!

I am using a battery booster (as it seems the same as you use), i have the battery jumpers connected, all the resistors and caps for the battery measurement.
It is just wired that it functions while the nrf24 is powered separately. maybe i got some bad radios?
One more question: the cap just below the booster. is this necessary to reduce the noice for the radio? might that help and if yes what size do you recommend? i didn't solder any cap yet there.

"Did you by any chance connect both batteries and ftdi Vcc at the same time?"
Yes! I did try this as well. Same results...
I should also mention i got my Arduino Pro mini battery powered hacked. So no more LED and Voltage regulator. But then again i also tried it with a untouched one.

just a quick update.

i ran some more tests with different radios and a 10uf electroltyte cap on the booster. And some different batteries.
Heureka! It works. For now. It is running now with a 3.7v lipo battery without the voltage regulator. Does anybody know if this is safe in the long run?

Thanks for clarifications

Awesome forum!