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 second one runs whether the pack is working or sitting idle. Calendar aging is the slow chemical wind-down that happens with time alone, and its speed is set mainly by temperature and by the state of charge the pack sits at while it waits. Keep a lithium pack hot and it ages faster doing nothing than a cool pack does under daily use, because the same side reactions that slowly consume the cell's active material run quicker the warmer it gets, roughly the way every chemical process speeds up with heat. A pack stored full and warm is in the worst of both worlds; the high voltage and the high temperature together push those parasitic reactions hardest. This is the quiet reason two identical batteries diverge. One lives in a climate-controlled aisle and gets parked at a moderate charge over the weekend; the other sits near a loading door that bakes in afternoon sun and gets left topped to the ceiling every Friday. They will not reach end of life together, and no cycle count printed on either one predicts the gap, because the cycle test held temperature constant precisely to keep this variable out of the result. When a vendor quotes a lifespan, the honest follow-up is not how many cycles but at what depth, at what temperature, and held at what charge between uses, because those three answers move the real number around more than the headline ever admits.
Reading the number like a buyer
A cycle rating is a comparison tool, not a calendar. Used to line up two packs tested the same way, it tells you something real. Read as a guarantee of years in your building, it sets you up to feel cheated.
The conditions behind the number are the number.
The questions that pull the rating back to earth are short ones. What depth of discharge was the test run at. What temperature. What capacity threshold counted as the end. A pack quoted at a deep daily drain and a mild lab temperature is being described at its kindest, and your warehouse is rarely as kind as a test chamber set to room temperature.
None of this makes the number a lie. It makes it a conditional. The battery genuinely can hit that count if the depth stays moderate, the heat stays off, and the charge habits stay sane, which is also a fair description of how to make any lithium pack last. The spec is less a fixed property of the battery than a description of the gentlest life it could lead, printed as if it were a fact about the hardware.
A fleet that wants the big number in the real world earns it through how it runs the trucks, not through which datasheet it bought. The pack sets the ceiling; the operation decides how close you climb.
What to specify instead
Rather than chase the largest cycle figure, pin down the duty: how deep the shifts run the pack, how hot the space gets, whether trucks sit full over weekends. Match the chemistry and the sizing to that, and the lifespan follows from conditions you control rather than from a promise you cannot reproduce.
Oversizing slightly so each shift is a shallower bite of the pack is often cheaper over the years than buying exactly enough capacity and then draining it hard every single day.
The builders who talk this way, asking about your shifts and your room before quoting a life, are the ones to listen to. Shinko Power sizes its traction battery solutions to the duty rather than to the brochure, which is where real lifespan is decided.