Robert M. Gary wrote:
When I turn on a lot of accessories on my Mooney F '76 I can drop the
bus voltage down to around 13.6. My A&P says 13.6 is normal with
accessories on. Does this sound right?

How dare you doubt the word of your A&P? Don't you know that every A&P
candidate is individually interviewed by an FAA inspector before he's
even allowed to take the written test, and those who are unworthy are
weeded out? ( for the sarcasm impaired )

Seriously, 13.6 volts under load is not unusual.

In theory, the system should be 14 V, and you are allowed a drop of 2%
of that to the main bus, for a minimum voltage of 13.72 V. Now, how
exactly do you think your 20+ year old (by design) regulator holds the
voltage? Think it might be 0.1 V off? Because that's all it would
take. Think it's absolutely insensitive to load (a true voltage
regulator with zero temperature and current dependence)? Think again.
That level of stability is not necessary and generally not present.
Typically the regulator will give you 14 +/- 0.2 V.

At 13.6V, your battery will charge just fine and your accessories will
run. So watch it, and as long as it stays where it is, don't worry
about it.

Michael