Before your battery is swapped out, if you charge the car until it stops (however many bars it's at now), then unplug and wait a few hours, then plug it back in, will it start charging, or does it just act the same as fully charged on any other car?
I think the meter is definitely SOC, and since the few bad cells are cutting off the charge early, the gauge is not going to be full. If all cells wore down evenly and were balanced, even with the reduced capacity, the gauge would show full since the pack would actually be at full charge (for the available capacity). Since these few cells have suffered faults, they may have lost a large portion of their capacity and are hitting the HVC. If the BMS could bring these cells down enough so they hit the same voltage as the rest of the pack near the top end, the gauge may go back to 16 bars, but you would lose bars and miles fast because the whole pack would be down to the lowest capacity cell.
The car watches voltage as well, so that could explain how the last 2 bars disappear so quickly on normally functioning vehicles. NiMH's (and I believe lithiums, as well) hold a fairly linear and narrow voltage throughout most of its discharge, but right at the end, voltage sags rather quickly to LVC. The BMS sees voltage starting to go down faster, so it cuts away at the last bar or two, prompting the driver to shut off extras (HVAC, heated seat, radio) and slow down. Since power draw is reduced (most likely), the voltage will come up a little, resulting in more available energy without damage to the battery, leaving us with more "no-bar" reserve. I noticed on my car, even without any bars, I had 3 miles remaining and no turtle.
