Nikon SB 900 ext battery port specs
I am trying to find the electrical requirements for the Nikon SB 900 ext battery port:
What are the minimum and maximum input voltages at the port?
I would like to use a rechargeable Lipo battery pack (from a hobby / RC store)
You need a power supply, not just a battery. The voltage is in the ballpark of 325 volts, to directly charge the flash capacitor.
Instead, you definitely need a SB-900 power pack, like these: