Which firmware you are on now?

You're lucky, I was not provided with the software option to update the battery separately. I Had to send my entire scooter to Segway for their repair.

Firmware
 

Hello
Main Firmware is 0.1.3.9 (since today)
Battery is 0.1.3.6

Interesting, I was at version 1.3. 3 when my external battery stopped being recognized by my main scooter and therefore the software itself stopped seeing the battery. I purchase the 2nd battery brand new only two weeks earlier and everything was working okay. I was there for never able to even have the option to upgrade beyond 1.3.3.

after this fiasco, I am very hesitant to simply click update on the app as this small selection is what led to my entire scooter solution being bricked. I have been without a scooter for over 2 months and it is still at Segway being repaired. I have a suspicion that they received more scooters with firmware update error 50 than they are leading on about.

IPhone
 

I was one step away to send it back.
I always used may Andorid Phone. No update appeared on the phone.
Only the outdates message.
I installed the segway APP on the Iphone 8 plus from my wife logged in and got the message an update is available...

Maybe this work for you to
 

I recived yesterday my extra battery, when i put it it gives to me error 50. I removed the battery, turned on the scooter, sync whith my android phone an then i conect my extra battery to the scooter. On my phone was displayed a mesage that i have bms upgrade i pick ok. The bms was upgrated (from 1.3.0.3 to 0.6 if i remembered it correctly) and all works fine whith 2 batteries. I think the error es 50 hapens when the 2 bms dont has the same firmware.