Ok.
Thanks for the help. If I understand it right it is not recommend to power the NP2 via the 5V pin. So I think I have find a alternative to powering the NP2. I find several boards that are able to pull up the voltage. So I will take the 7.2V of the accu pack an pull it up to 9V and connected that to the connector barrel of the NP2. This boards only costs 4-5€ so I think thats a save solution.