The alternator windings are energized by voltage from the battery, creating
a magnetic field that will begin delivering electricity as soon as the
engine starts. These windings are connected directly across the battery
through the BAT/ALT switch. When you leave the ALT side of the switch off,
these windings are no longer connected across the battery and do not present
a load to it. When the engine starts and you turn the ALT side on, you get
the electricity you need. My advice is to leave it OFF until needed.

Bob Gardner

"Lakeview Bill" wrote in message
.. .
On an aircraft with separate "battery" and "alternator" switches, should
you
turn on BAT and leave ALT off during engine start, or should you turn them
both on prior to start?

A little bit of the "why" on this would be nice also...