Li-ion cells come with undervoltage protection circuits - little integrated thingies that open up the circuit when the voltage across the cell drops below 2.7V or so. What sort of a switch is that? I've been thinking, if a cell is inside a large series pack - a dozen of cells for a hobbyist, or a hundred cells for an electric car - won't that switch be subjected to the entire voltage of the pack upon it's opening for the weakest cell? If so, what is the breakdown voltage of these switches, i.e. in 18650 cells, where can i look it up? If not, how does that protection work? I never seen such figures given in battery datasheets, so maybe i've missed the big idea?