I measured some more things. My battery is in my trunk. Measuring across the battery, the voltage dips to about 10.1V. Measuring between the fuse block and the chassis under the hood, it dips to 7.72V. So it would appear that there is something wrong with the wiring somewhere between the trunk and the engine compartment. Then again, that's a long cable and a lot of current. Maybe a 2.5V drop across that much cabling is "normal".