TSquared sent me a video of his FX-3 runup a week ago showing a rapid voltage drop when doing a runup with key to R and backup ignition ON. We figured his backup battery was bad so he has a new one coming. Today I went for a short flight after installing a new starter battery and noticed the same. His plane is 2 years old, mine is essentially new, battery has been in for about a year now but not flown until this past June.
So the question is, why when turning on the backup ignition is the voltage (right side of the two voltages) drops like a rock?
https://youtu.be/mPhzREYnc70