Why a spare is worth having
Every AXS derailleur and shifter runs on the same battery, and they swap between components in seconds without tools. So if the rear derailleur dies mid-ride, you can pull the battery off the front and finish the ride shifting at the back — which is the half that matters.
That interchangeability is the argument for a spare in the jersey pocket rather than a second charger at home.
Charge them before a big ride rather than after. Battery life is measured in weeks of normal riding, which is exactly long enough to forget about it completely. Part of the SRAM drivetrain range.
