@Eric-Katzfey I updated to SDK 1.6.0, which fixed the power display issue. I was still getting no valid local position preflight fail, but after I ran apt update && apt upgrade, things seemed to work.
Good tip. For anyone testing without the GPS module attached, setting SYS_HAS_MAG=0 and EKF2_MAG_TYPE=5 seems to be the key part since the compass is on the GPS board. I was also looking at some compass-related references on 123compass.org while trying to understand the magnetometer side of it.