^ Charging AAs is no problem with an 8-slot charger, or even 2 4-slot chargers. As mentioned previously, the 8 AA sled is a backup to the USB-C battery, so they don't need much time on the charger anyway. AAs also have the advantage of being cheap, easily obtainable, compact, and useful for a wide range of other devices. And the 8 AA sled is pretty small and the same width as the MixPre, so easy for the bag too...