A battery rated for 5000 cycles is making a promise about a lab, not your warehouse

The cycle number on a lithium battery's spec sheet is true and almost useless, because it describes a life the battery will live only in a temperature-controlled lab being cycled gently by a machine that never has a bad day. A cycle, in that test, means a full charge and a full discharge under mild, steady conditions, repeated until the pack fades to some fraction of its original capacity, often eighty percent. Your warehouse does none of that. It charges in bursts, discharges to whatever the shift demanded, bakes the pack in summer and chills it in winter, and counts a cycle as whatever happened between two plug-ins. Depth is the lever nobody quotes The single biggest mover of cycle count is how deep you run the pack on each outing, and that figure almost never shares the page with the headline number that sells the battery. The relationship is steeply nonlinear, which is the part that surprises people. Drain a lithium pack to nearly empty every time and you spend cycles fast. Use the top half and tuck it back on charge, and the same cell can deliver many times the number of shallow cycles before reaching the same faded state. The chemistry is mechanical about it: every deep swing stretches and contracts the electrode structures further, and the wider the swing the more wear each one inflicts. Two fleets on identical batteries can see lifespans years apart purely from how hard they drain them. This is why opportunity charging does double duty. It keeps the truck running, and it keeps each cycle shallow, which stretches the pack's life as a side effect. It also means a published cycle figure measured at full depth understates what a top-up fleet will see, while a figure measured shallow oversells what a run-it-flat operation will get. The same battery, the same number, two outcomes the sheet never warned you about. You have to know the test depth to know what the promise means. Heat is the other clock Cycles are only one of two clocks ticking on a battery, and the s