This little gizmo is the cause of an awful lot of unhappiness with the Model S.
I don't own a Model S, but I do know a little bit about batteries - and while most of my work is with lithium battery packs, I also know a bit about lead acid batteries, as my office uses a good sized bank of them (about 225Ah at 48V, depending on rate) for solar energy storage. No, I couldn't get my hands on a PowerWall, and no, one wouldn't even be useful to me voltage-wise. Though if you have one laying around you'd be willing to part with, let me know...
Anyway. I was wandering around the internet and came across something interesting.
I've got, on my flash chips, this tiny little file that, on analysis, turns out to be a few days worth of data log from a Model S 12V battery system in late 2016. Voltage, amperage into or out of the battery, and some surrounding data about charge state and the like. Rumor has it that the power settings are "Energy Saving : Off" & "Always Connected : On."
So, in I dive! Chart a course to graphs!