I am coming to the conclusion that everything -- except the three odometers -- is subject to random voltage variations, or other non-linear analog measurements. I've driven the car pretty hard today, starting with a 100% charge and traveling 87.1 miles, mostly freeway, more than a third of it at 65-70 mph, almost all of it with A/C on. That's not too shabby, and I must say I am pleasantly surprised. Oh, my energy economy for the day? Only 4.0.
But, here's the reason for this post. I was 15 miles from home with one bar showing when I got the "low battery" warning. 'Oh, oh', I thought, 'this is going to be a squeaker.' I decided to take the old highway home rather than the freeway. It has half a dozen traffic signals and speed limits of 45 or 50 most of the way. Since my wife was with me, and I was determined not to strand her, I held my speed to 40 and cut the A/C, leaving the fan on. Ten miles later I still, to my amazement, had one bar showing, so I sped up to 45. Guess what -- I pulled in and stopped at home and still had one bar showing, though the guessometer was flashing 4. Naturally, no "very low" warning.
Fifteen miles after the low battery warning without even losing bar 1?? When we normally think of that warning as coming in the middle, or near the end of bar 1? It seems to me the BMS or dash computer must have seen a momentary voltage drop from the battery, and panicked. It seems to me I dropped from two bars to one prematurely, and got that low battery warning sooner than I should have. So, good luck on calculating kWh/bar, Andy. You may have to tack "+/-0.5" on your answer.
Incidentally, I was within a mile of South County Nissan in Gilroy when I got the warning, and I could have panicked too, insisting we stop there to juice up for at least half an hour. I'm glad I didn't; my wife would have hated it, and it obviously wasn't needed.
End of April 2013: Traded my 2011 SL for a 2013 S with charge pkg.