Battery Life Estimator

Battery life refers to how long a battery can power a device before it needs to be recharged. It depends on the battery's total capacity (measured in mAh or Ah), the device's power consumption, and real-world factors like temperature, battery age, and discharge depth. This tool estimates runtime based on those inputs.

The core formula is: Battery Life (hours) = Usable Capacity (mAh) ÷ Average Consumption (mA). Usable capacity is the total capacity minus the discharge safety margin — for example, with a 20% margin on a 5000 mAh battery, you get 4000 mAh of usable charge. If your consumption is in watts, divide by voltage first to get milliamps.

Sleep mode can dramatically extend battery life. When a device cycles between active use and a low-power sleep state, the average current draw drops significantly. This calculator lets you enter active time, sleep time, and sleep current so it can compute a weighted average consumption and give you a more accurate runtime estimate.

The discharge safety margin is the percentage of battery capacity you intentionally avoid using to protect battery health and longevity. For most lithium-ion batteries, 20% is recommended — meaning you use only 80% of the rated capacity. Deeply discharging a battery repeatedly can significantly shorten its overall lifespan.

With a 20% safety margin, a 4500 mAh battery has 3600 mAh of usable capacity. At an average draw of 300 mA, it would last 12 hours. At 150 mA (light use), it could last 24 hours. Actual runtime varies based on your device's real-world consumption and environmental conditions.

Yes. Select the appropriate battery type (Gel, AGM, or Flooded Lead Acid) and enter your battery's capacity in Ah (switch the unit selector). Enter your device's current draw in amps or watts. Lead-acid batteries typically use a higher safety margin (around 50%) since deep discharging them causes permanent damage.

The easiest way is to check the device's datasheet or specification sheet, which usually lists typical current consumption in mA or watts. You can also measure it with a multimeter in series with the power supply. If your device's specs list wattage, divide watts by voltage to get amps (e.g., 6W ÷ 12V = 0.5A = 500 mA).

Battery life calculators provide a reliable theoretical estimate, but real-world runtime can vary due to battery age, ambient temperature, load spikes, internal resistance, and the accuracy of the capacity rating. Treat the result as a useful guideline and plan for a 10–20% real-world variance on top of the safety margin already built in.