The Commander's car likely has a dead cell in the battery and it should be replaced in the near future. Full charge is 13.8 volts or 2.6 volts per cell. Remove a cell from the equation and you get 11.2 volts.
At the very least, he should make sure the electrolyte level is good on all cells. If one is pretty low, add distilled level to take the level up enough to cover the plates and then some (like 1/2" over the plates). If you do find and take care of a low one, you're likely to get a better reading on the voltmeter without even driving the car.
There are a number of reasons you could be getting 13.33 volts instead of 13.8. As the battery approaches full charge, the alternator should start to taper off, so it can take quite a while to get that last half volt. Also, if a door was open (interior lights) or there's an under-hood light, that'll cause a small voltage drop. Or if the car's new enough, the computer is constantly drawing juice.
I've got a BMW motorcycle that's so under-batteried and over-computerized that if I let it sit for 2 weeks, the battery is completely drained. I really need to get a couple dozen trickle-chargers for these darned things that sit for such long periods of time. Might save hundreds on the Spring ritual of replacing batteries at my place.
Edit: 11+ volts is more than enough for a car to start well. It's all a matter of how much power is stored in the remaining good cells. You can have as many as 2 completely out-of-the-loop cells (10.4 volts) and as long as the 4 good ones are really good, the only difference will be the starter not spinning quite as fast, and it'd be such a subtle difference that it likely wouldn't be noticed. Especially with an engine that lights right up.
