Multimeters are Cool; Used Minivans are Not

My dad is an electrical / mechanical / power-systems engineer who has taught me about volts, amps, ohms, etc. about once a year since I was a baby. He needs to keep reminding me because my knowledge of the subject fades faster than a cheap alkaline battery in a GoPro Helmet Camera.

Unlike a battery, though, which fades from overuse, my memory of electrical stuff fades from lack of use. Maybe that's what Dad was trying to prevent when he bought me a digital multimeter for my 30th birthday this year. It was apropos considering the slew of electrical problems I'd been having with my station wagon. When I replaced that lemon of a car with a less-old minivan last week I was looking forward to forgetting everything about electricity once again. I think you can see where this is going...

Today the @#$% minivan wouldn't start! At least not until I turned off the radio and the fan, took several deep breaths, and turned the key juuuust right. So I backed the car into my driveway in an easy-to-jumpstart-if-necessary position, took my multimeter out of the box for the first time, and called Pa' for my yearly electrical engineering refresher course. Here's what he said I should do to see if there's something wrong with the battery, cables, or charging system:

1. Set the multimeter to volts and measure the voltage across the battery terminals when the car is not running. It should be around 12.5. (It was.)
2. Have someone turn the key to start the car while you continue measuring the voltage. If it drops significantly below 12.5, like down to around 9, that's bad. (It didn't.)
3. Continue to measure the voltage when the car is running. It should be 14 or more to be properly charging the battery. (Mine was 13.55. That might mean the alternator [the thing that charges the battery] isn't working quite right.)
4. If the voltage is kinda low when the car is idling, rev the engine a bit and see if that brings it above 14. (I haven't tried that yet since I sent my car-starting assistant home before Dad recommended that test.)
5. Also, while the car is running, test if the battery cables are bad by putting the black (-) multimeter terminal on the bare metal of the engine and the red (+) one on the cable attaching to the (+) battery terminal. If that's lower than the voltage just across the battery terminals, there might be too much resistance in the cables. (It wasn't.)

Conclusions:

1. My battery and cables are probably ok but my alternator might be going. I hope the alternator IS bad, because if it's not there could be a harder-to-diagnose and more-expensive-to-fix problem with the electrical system, putting me in the same place I was with my old car last year when its hellish behavior began.
2. I might actually remember about electricity now, thanks to all this hands-on learning experience.
3. I will probably stall on the side of the road tomorrow.