The Phase One XT is designed from the ground up to be a field camera, and when you take a camera into the field for long periods power is always a concern.
The Internal Battery
The Phase One XT body and Phase One XT lenses draw their power from the Phase One IQ4 digital back. That means the entire system requires only a single battery (inserted into the Phase One IQ4) for power; the XT itself does not have or need a battery. The battery that goes in the IQ4 weighs just 100 grams and costs just $70, making it easy to pack a few for a longer trip.
External Power
The IQ4 Infinity Platform accepts power through its USB-C port and Ethernet port (via POE). In the field, that means you can use one of any number of external power packs rather than changing out the internal battery. These power packs are relatively inexpensive and commonly used to charge phones while on the road, and so are often already in a photographers travel kit.
The Phase One IQ4 USB-C port can also be used to extend the power of an IQ4 to an accessory that draws power over USB. For example, the Phase One XT is compatible with Cambo WRS lens panels including the one for Canon lenses such as the Canon 17TSE. That panel has a small (non removable) battery which is charged by USB Mini; that battery has quite a long life, since it goes to sleep when not in use and only draws meaningful power when making changes to the aperture. But it’s possible that on a longer trip you’ll find you’re low on battery on that lens panel. Not to worry! If you run a cable from the USB-C port on the IQ4 and the USB Micro port on the Canon lens adapter the IQ4 will charge the Canon lens adapter.