Note that if you're at 15% SOC ("0 miles" of range) and you leave the car sitting for six months in extreme (e.g., very much below freezing, or very much above 100-ish F / 40-ish C) temperatures, you still run some risk of killing the batteries. Leaving it for a month should be fine though. Unlike the Roadster, there should be no "parasitic drain" on the li-ion batteries.sourceSpeed-sensitive steering assistance is provided by an electrohydraulic system that runs on the car’s 12-volt system. This low-voltage system powers the on-board accessories, lighting, and infotainment system, and stores power in a conventional lead-acid battery. The roof of the Karma has solar panels that feed the system with up to 120 watts of power on sunny days. While this electricity never powers the wheels directly, it can reduce the amount of low-voltage power pulled from the high-voltage system, and could, in theory, add up to 200 miles of additional range per year. Cool, yes, but it’s mostly there to make a statement, we suspect.
Basically, everything that does "power drain while off" is run off this separate, conventional-car system. The li-ion batteries are free to sustain themselves for long periods with no draw at all.