You could always borrow a set of batteries from a local Segway owner/dealer.
That would allow you to power up your machine.
Then you will need to do the firmware update.
Originally only Segway ( online ) plus special equipment at the local dealer could do this.
Now that Segway are no longer in business, i am unsure how this might work.
Others may be able to answer that for you.
Good Luck
Michael
www.dgbint.com