Capacity in mAh alone does not tell you runtime—you need voltage and load watts. This guide walks through the battery runtime calculator: mAh, nominal V, and power draw for hours of operation.
Benefits
- Wh = (mAh ÷ 1,000) × V, then runtime h = Wh ÷ W.
- Works for Li-ion cells, power banks, and small DC loads.
- Shows energy in Wh alongside duration for fair pack comparisons.
How it works
- Enter battery capacity in mAh from the label or spec sheet.
- Add nominal voltage (3.7 V cell, 12 V AGM, etc.).
- Enter steady load in watts—read estimated runtime in hours or minutes.
FAQ
How does the battery runtime calculator work?
Convert mAh to Wh: Wh = (mAh ÷ 1,000) × V. Divide Wh by load watts for hours. Example: 5,000 mAh at 3.7 V → 18.5 Wh; at 10 W draw → ~1.85 hours. Lower watts extend runtime linearly.
Why convert mAh to Wh before dividing by watts?
mAh is charge, not energy—voltage completes the picture. A 10,000 mAh 3.7 V phone pack (37 Wh) and a 5,000 mAh 7.4 V pack (37 Wh) deliver the same runtime at the same watt load despite different mAh ratings.
Should I derate the calculated runtime?
Yes for planning—heat, age, and high discharge rates reduce usable capacity. Derate 15–20% for outdoor gear, aged cells, or continuous max draw. Pair with Battery Charging Time to plan recharge after the discharge window.
Technical specifications
- Wh = (mAh ÷ 1,000) × V.
- Runtime (h) = Wh ÷ load_W.
- Assumes near-constant DC or inverter load in watts.
- Related: battery-runtime, ah-to-wh, battery-charging-time, ups-runtime.