Although multiplying amp-hours by volts looks about right, it's not strictly correct, because lithium-ion battery discharge isn't linear. This image was plucked from a post by DucRider in another thread (
https://www.insideevsforum.com/community/index.php?threads/battery-capacity-test-results.5836/page-4). Once the cells get significantly below 3V, you won't draw much current from them (and you'll risk permanent damage).
You might find reading through the thread interesting, Sailorman.
I cited this article somewhere in the thread, and found it useful reading:
https://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries
Table 4 to me was interesting. It says that if you cap cell voltages at 3.9V instead of 4V, battery life expressed in charge cycles doubles. There are many grains of salt to be taken here -- variations in battery chemistry, what end of life meant for the batteries tested, etc. -- but I fully expect that Honda traded away some battery life for higher EV range, since they don't expect the typical owner to own the car for ten years or more.
And apropos to battery life, this article turned up in my feed this morning:
https://electrek.co/2019/12/14/8-lessons-about-ev-battery-health-from-6300-electric-cars/
I haven't drilled down into the data on which it's based except to see that no Honda Claritys are in the dataset, though there are other PHEVs among the EVs.
As for our Clarity, Honda of Bellevue didn't provide me with the capacity number in the PDI report when we bought the car in May 2018, and at its A01 service in May 2019, the tech I talked to midunderstood what I wanted and by the time I learned it wasn't done, it was too late in the day and I needed to take the car home. In October 2019, after our long trip, I had another service and they finally read the battery capacity: 51.7 Ah, which would be a 6% drop from the nominal. I was a bit bummed about that, though we get plenty of range: around 40 miles in our current Seattle weather of mid-forties Fahrenheit, and 50-60 miles real range in the summer.
I generally charged to Honda's 100% (following the manual and some early recommendations which I'm not sure I can find now). In particular, I did leave the battery fully charged for a 5 week period while we were overseas, so that might have dinged the capacity.
But I also don't know what the capacity was when the car left the lot. The dealer is relatively PHEV-savvy (for a Honda dealer, which is a pretty low bar) and the car had plenty of charge when we test drove it, so I'm optimistic they didn't let the battery go to zero in the 3 months from manufacture to sale.
I also wonder how much we should trust the capacity number the car tells us. As Landshark says, it's likely based on a measure of voltage drop as a function of loss of charge (time multiplied by average current), but is it continuously measuring discharge current or just for intervals? If the latter, at what point(s) in the discharge curve? How accurately? How many measurements is it averaging? Is battery temperature taken into account (i.e. does the capacity number drop in the winter and rise again in the summer)?
Here's hoping Autel comes through with a reasonably cheap OBD-II tool that displays capacity so we can see the number more frequently.