Amp-Hour Battery Life Calculator

Whether you are planning a campervan or boat setup, a solar battery bank, an off-grid cabin, a UPS or a portable power station, the question is always the same: how long will the battery actually run my gear? This calculator answers it clearly from four inputs. Enter the battery's amp-hour capacity, its voltage, the load you want to run in watts, and the usable depth of discharge, and it returns the realistic runtime in hours, along with the total and usable energy in watt-hours. The method is the one professionals use. Amp-hours on their own only describe capacity at a given voltage, so the calculator first multiplies them by the voltage to get watt-hours, the true measure of stored energy, then applies the usable fraction you can safely draw, and finally divides by the load in watts to give the time. The depth of discharge matters more than people expect: lead-acid and AGM batteries are usually limited to around half their capacity to protect their lifespan, while lithium batteries such as LiFePO4 often allow eighty to one hundred percent, so two batteries with the same amp-hour label can deliver very different real-world runtimes. Working in watt-hours also lets you mix and match: a load rated in watts can be run from a battery of any voltage, and you can compare a 12 volt and a 24 volt bank on equal terms. Use it to size a battery for an overnight load, to check whether your existing bank will last a trip, or to compare options before you buy. Real runtime is also affected by temperature, age and discharge rate, so treat the result as a solid planning estimate. The method and a worked example are below.

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A planning estimate. Real runtime also depends on temperature, battery age, and how fast you discharge. Estimate only.