Well, was hoping to post this much sooner and have much more information but alas I dont have either.
I have continued to monitor the voltages and found that there are a few things that seem to be developing as trends. For anyone else out there that is also monitoring their 12 volt battery, please chime in with your observations so we can put our heads together to get something more definitive.
I also tried to find out the feasibility of replacing the lead acid battery with Li since Li is much more amenable to being the the middle SOC ranges but not much response there and guessing most would have discounted it due to a much higher cost.
But a few things that I have seemed to notice;
** leaving the car plugged in after charge is complete lowers the voltage faster. Not able to double check this due to driving demands but on the few occasions I was able to let the LEAF sit 10+ hours plugged in, the voltages were in the 12.15-12.2 range.
**Temperature is playing a part. We are just finishing up a cold snap and it was parked outside with temps in the mid 20's and seeing voltages dropping much faster. In one case to 12.14 volts after just 4 hours when normally I would see about 12.4 or so. So park it in the garage if you can. that extra 10 º of warmth might make all the difference in world.
Another thing; once I checked it first thing in morning in garage; voltage 12.23 volts. then checked it a few hours later after Sun came up and there was a lot of radiant heat (have window where morning Sun shines into garage) where temps were a good 15º warmer. and voltage had risen to 12.42 volts.
** The Voltage drop, at least in my case rarely goes below 12.2 volts but that is still too low. The voltage drop rate seems to level off after about 12 hours or so so guessing that is a semi decent indication of my battery's overall state of health which is not very good considering the battery is 2 days short of 2 years old in a climate that is nearly ideal for lead acid battery health (yes, unfortunately once again, Phoenix will see a shorter lifetime here as well)
Solution; Well most are investigating simply replacing the OEM battery with a more robust one able to weather the deep discharges a bit better.
One thing I would definitely do is have a jump box on hand charged and ready to go. I have used one for years while camping to charge my cellphone and that kind of stuff so I have a few in various states of readiness. If maintained and boost charged once or twice a month when not used, they are usually good for 4-5 years.
They are sealed units so leakage is not a problem so carrying it around in the car (not during Summer!) is doable plus they are fairly light so even people of modest physical capabilities can handle them easily. The unit is too light for my scale to weigh it separately but it works out to be about 6 lbs.
I think my last one came from Harbor Freight and a scan of their online catalog looks like one can be had for under $50.
Here is mine. The Harbor Freight one is a bit nicer than mine since it has a light and all, but then again, I think I paid like $25 for this one at Big Lots about 3-4 years ago...
The other thing is that unless your LEAF is going to be sitting in extremely cold or hot weather for more than a few days, you should have little to worry about. Since I drive my LEAF nearly daily, I am thinking that I could eek out my current battery for years without issue. Despite that, I have definitely been maintaining my jump box a lot more than usual lately as you can see by the pix, it is plugged in which I do a few hours a month...