What does a kilowatt hour look like?
Given how popular (and damn near impossible to discern) unsafe and unprotected lithium-ion batteries are, the idea of making a homegrown power wall terrifies me in ways I can&#x27;t even begin to contemplate.<p>An 18650 battery, if combusted, can produce hydrofluoric acid with just water vapor in the air (or the water in your lungs) if they use lithium hexafluorophosphate as the electrolyte. Hydrofluoric acid can and will cause permanent damage to lung tissue if inhaled, and nasty, nasty chemical burns to exposed skin. 18650 batteries are supposed to have several failsafes to prevent thermal runaway, but counterfeit batteries can lack those failsafes. Not to mention, in some laptop battery packs, the protection was pack-wide, and not in individual cells. Not knowing the chemistry of the cells or the state of the protection circuitry of the battery would make me very nervous. Maybe someone else can provide more detail on how to test them safely.