I now carry a spare coin battery for the axs shifters. Yeah, they last years, but of the three sets of axs shifters I have, one of them has started draining the battery in a matter of weeks and it goes dead without warning. Its outside of warranty so I've just accepted that I'll change the battery frequently and always carry spares on the bike.
Even if you don't have this issue, it doesn't hurt to keep one in the bag.
I was thinking a cheap actual AXS battery! But yeah coin cell definitely a good shout, I have used one for a dead HR monitor and separately power meter mid-ride in the past!
I now carry a spare coin battery for the axs shifters. Yeah, they last years, but of the three sets of axs shifters I have, one of them has started draining the battery in a matter of weeks and it goes dead without warning. Its outside of warranty so I've just accepted that I'll change the battery frequently and always carry spares on the bike.
Even if you don't have this issue, it doesn't hurt to keep one in the bag.