A friends AWD magna is having troubles.
the car is stalling on on start up. and only gets going when you hit the pedal to stop it from stalling.
its not every time but doing it on a regular basis.
they took it into a mits dealer and they "reset the ECU"
but this has done nothing.
i told them to test battery, when the car is running, its putting out almost 20V
can i get get away with just just the regulator, or best to replace the alternator?

The electrics and electronics on the Magna don't appreciate 20V. Check the battery voltage with a different multimeter to see if it is in fact getting 20V.

The battery is probably bubbling away furiously at that voltage. Not good for it.

Tell your friend to stop driving it until you can replace the reg or alternator, don't want to start blowing the ECU/TCU etc. , now do we?

Yeah. Is it worth just chucking in a 2nd hand alternator or replacing the voltage regulator?
I've herd before that replacing the regulator is just a temp fix

It is well known that a worn out battery will cause the start and immediate stall problem with a Magna.
Car will then start OK on the second attempt.
If is doing something different look at things like the ISC, clean throttle body etc.
Try swapping to a newer battery to check this out.
Basically I have found that a Magna battery has had it after 3 years.

20V when the engine is running points toward a stuffed alternator, for sure it will boil the battery.
Gerry

Try a regulator if its cheaper, and get a $4.99 multimeter and wire it to a fused battery connection and sit it in the ashtray to watch when the voltage goes up again.

hope you are not driving it, get new voltage regulator or new altenator mate before you cook battery and other electrics cheers

If the batteries got issues it may cause the alternator to over only. Got a tester batt you can use?