James I'm looking to experiment and put GOS on a phone with a removable battery.
GrapheneOS is designed to run on devices with strong hardware and firmware security. If a device doesn't have that, the result of a port would not be GrapheneOS. Here is a list of device requirements (including manufacturer commitments): https://grapheneos.org/faq#future-devices
GrapheneOS is derived from AOSP. If AOSP is available for a device it would be possible to port some GrapheneOS features (though not full security) to AOSP for that device. The DivestOS project has done that for some devices, and perhaps you might want to work on that.