Well I don't know where to post there but here goes:
A buddy off mine since back in high school is on a fire dept. on the left coast. They had a problem with their headset controller switching channels when they started the fire truck. The measured 9V when cranking, the headset manufacturer said "There's your problem, that's too much drop".
So I set out to measure what the battery voltage looks like during cranking. I took a 8 megasample digital scope and captures the event, then went looking for dips and spikes.
The 1st shot is a 400 HP Detroit in a fire engine. Note that the battery got down to 7.8 volts. The waveform you see from divisions 3 to 6 corresponds with the "cranking" rhythm during cranking. At 6 divisions, the engine had started and you see the starter free-wheeling. Then the guy starting it takes his finger of the button, and you see the alternator kick in and the battery voltage go up.
I was very surprised to see no spikes over 16 volts on the system (you have to zoom in to see them). I had been told years ago that you would see 100V spikes for a microsecond or so. BTW, I was sampling every 250 nS.
The next shot is a spike form the charger that is in the truck when it is on shore power. It has a 17 volts spike, but it is very short lived. I upped the sampling time to 5 nS for this.
The 3rd shot is starting a F350. Very similar patterns to the big engine, but it took about .75 seconds for the alternator to kick in. Minimum voltage was 7.6 volts for a brief instant.
The "broad width" of the trace is brush noise during starter, and alternator whine at the end.
So if you ever wanted to see what's going on when you crank, here it is.