I've done plenty of "bottom of the capacity" testing in my '13 and 1 bar on the battery gauge is roughly 5% where on the '13 and newer models, the capacity gauge drops below 6% and then turns into --- to let you know it's just guessing afterwards
But really, the vehicle does know what it has. I've driven mine with LeafSpy until about 1% and then limp over to Nissan HQ, plug in the QC and it starts charging right at 1% like LeafSpy shows.
On the 2011, 2012 models, they don't have a capacity percent dash mode, but my guess is if you are down to 1 bar on the capacity, it's just below 6% capacity and when that final bar disappears (no bars), they are around the 3% capacity. That is the way it shows on the '13 anyway. Now, plugging into the QC, my only guess is that some math issues are making the QC think the remaining charge is higher than it should be and with no dash meter to check against, it can get kind of confusing to owners (hence why the '13 and newer models added that charge gauge to help make it less confusing).
I'm not sure how the vehicle communicates the charge % to the QC or if the QC is doing some calculation to guess at the remaining capacity. If anyone has a '12 SL w/QC in the Nissan HQ area, let me know, will be glad to hook up LeafSpy and the QC at Nissan HQ (free 24/7) to play around with some capacity testing.