Checked a multimeter - power adapter is 8V at the screws. I also checked the voltage on the original and replacement batteries and both are a tad more than 4V.
I did learn something though. I’ve been trying to source replacement batteries through Amazon and the voltage/wiring is completely wrong compared to the original batteries. However after testing my original battery I don’t think that it’s the problem - there’s something else going on with my panel.
The behavior is similar to this - does this mean something just spontaneously broke internally? IQ Panel 2 LED blinking green, screen dead