supposedly the battery in these will get an hour+ of playing with like 15-20 minutes of charge time, so even if you let it go too long you can still use one and charge it between sets.
you can also get a little separate charger and another battery to swap out.
i hate both of these options, and i already have a nice tuner, so i'm thinking about the 14 myself with an extra battery to replace my relay G50, which has been fine but not flawless, with the AAs being a pain.
Guitar Repair Gnome
Alpha Music, VA Beach