We seem to diverge from the original post.
"Many moons ago I was taught to only switch on the BATT side of the dual switches (on the Cessna's) and in the after start procedure then switch on the alternator to check that it is working in the correct sense.
Is their any merit in this system rather than switching on both at the same time prior to starting and then checking the alternator output. Maybe an engineer can shed some light if there is a technical issue at work here."
My response was to indicate that if you are out in the boondocks in a 182 with an almost flat battery, for whatever reason, you may increase the possibly of getting a start if you turn the alternator off before starting, and back on after starting of course.
This is a response from the school of hard knocks and may help someone some day.