Inline Vw motor, digifant electronics.  Same alternator as Vanagon, etc.
This alternator is about 4 yrs old now, sourced from Van Cafe. It has been
worked hard keeping 2 batteries charged through extensive prolonged
off-grid camping. I've gone through 3 standard starting batteries, often
draining the auxiliary battery charging electronics, etc.

Today my aux battery was low so I plugged my 12v power source for my lap
top into a power point that's wired to the engine battery.  The laptop's
battery was dead, but I figured the bigger engine battery would have the
juice to charge the computer and still fire up the van. Wrong, the laptop's
battery took most of the charge from the van.  Tried jumping.from the coach
battery but that one was dead, too.  Did a one-man push start and drove
around for half hour.  Starts right up again, but I put my multimeter
across the vehicle main and it reads just 13.2v engine idling with no
accessories on.  Pretty low, according to Bentley.  Would that be
Reg/brushes ? in that time span and the use cycle?

Is the test just to get some new brushes and stick em in, then check the
battery input again?

Thanks, Don H.