Lakeview Bill wrote:
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...

What does the POH say? The instructions (and posssibly some insight)
will be there.

As a rule, the ALT is left off until the engine is running to avoid
power spikes.