It seems like it should be easy, but that isn't necessarily so. In CA this summer, we've had much lower temps than usual. I was pretty sure that one more summer would do the job for me, but summer's over, and that ninth bar clings stubbornly.
Many of the proposed schemes actually have very little effect. Just running the battery down using A/C or heat does little. Yes, you can add a few charge/discharge cycles that way, but cycling causes relatively minor degradation. Heat is number one, and calendar aging is probably number two. To get the battery hot, you need two things... high ambient temps and hard use or lots of quick charging. If I had a QC port, and the nearest charger weren't 84 miles away, I'd try that.
After I complete my normal commute, my car only has about 4 kWh left, and that'll be shrinking as soon as I start using the heater this winter. So I'm pretty much stuck without enough energy left to heat up the battery.
I'm also convinced that capacity bar loss is inhibited by the car's firmware in cooler weather to prevent false indications due to temporary capacity loss caused by low battery temperature. My car lost the tenth bar this past April, even though the Ahr reading was low enough to qualify clear back
in October. I am afraid that the same thing will happen this fall/winter, and my warranty expires in January.
To top it off, we do not know exactly what triggers loss of the ninth bar. Judging from the bell-shaped distribution we see (peak of the bell-shaped curve is around 43.3 Ahr), a number of factors enter in. It's not just a simple Ahr or GID value; there's more to it than that. Some speculate that the car must remain below some capacity level for a prolonged period like 30 or 60 days. I think the battery needs to stay above some critical temperature for some time in order to permit bar loss. It's difficult to hit a target that is undefined...