I use the Foto4easy Dummy Battery with a npf plate or my field monitor. has a 5.5mm don't recall if it's 2.1 or 2.5mm barrel but it works reliably

https://www.amazon.com/Foto4easy-DMW-BLC12-Battery-Extendable-Panasonic/dp/B08G4MTMZZ/ref=mp_s_a_1_6?crid=2VE975PPACB4W&keywords=g85+dummy+battery&qid=1649019388&sprefix=g85+du%2Caps%2C108&sr=8-6