Can I install the Acousti-Phonic without a battery if I'm installing the Hexpander too?Updated a month ago

Yes, but you will have no acoustic or mag output unless the Hexpander is plugged into a MIDI converter. This is only a practical option if you are always using the guitar with a MIDI converter, such as in studio or some stage setups. An on-board battery is essential for adding MIDI to a guitar that's used for a wide variety of applications.