What is the method for working out the runtime of a rechargeable LED work light?

Q: What is the method for working out the runtime of a rechargeable LED work light?

The runtime can be calculated by dividing the energy stored in the battery, given in watt-hours, by the real power consumption in watts and then multiplying the result by the usable system efficiency. For instance, if the battery has a capacity of 60Wh, it is powering a 20W light and the usable efficiency is 85 percent, the estimated runtime will be about 2.55 hours: 60 ÷ 20 × 0.85. The actual runtime will vary depending on the brightness setting, the efficiency of the driver, the ambient temperature, the limitations imposed by the battery management system, and the aging of the cells. When evaluating runtimes, you should use the tested figures at each brightness level rather than just the battery's amp-hour rating. The amp-hours cannot be compared directly when the battery voltages are different. Additionally, B2B buyers should verify the charging time, the cycle life data, whether the battery is replaceable, the indication of the charge state, the approvals for the charger, and the performance after repeated charge-and-discharge cycles.