Estimating Real Battery Runtime, Not the Rated Capacity

A battery’s watt-hour rating is a ceiling, not a promise. Voltage regulation, cable resistance, and safety margins all eat into the usable capacity before it ever reaches your camera or monitor. This tool converts a battery’s rated capacity and your equipment’s power draw into a realistic runtime estimate, accounting for regulator losses and a safety reserve so you’re not caught out mid-shoot.

Watt-Hours vs. Milliamp-Hours

Cinema batteries like V-mount and gold mount packs are usually rated in watt-hours (Wh), which already accounts for voltage and is directly comparable across different battery chemistries and voltages. Camcorder and mirrorless batteries are often rated in milliamp-hours (mAh) at a specific voltage instead. This tool accepts either: switch the capacity unit and enter the nominal voltage, and it converts mAh to watt-hours automatically for the runtime calculation.

Why Regulator Efficiency and Reserve Matter

Cameras and monitors don’t draw power directly from the raw battery voltage — a voltage regulator steps it down, and that conversion isn’t lossless. Regulator efficiency in the 85–95% range is typical. The reserve percentage models the safety margin you’d want to keep in hand: most crews don’t run a battery to zero, since voltage sag near depletion can cause equipment to cut out before the rated capacity is fully spent.

This tool is especially useful for:

• Camera assistants and gaffers planning how many batteries a shoot day requires.
• Anyone building a battery kit for a monitor, wireless system, or accessory with a known power draw.
• Productions checking coverage for a specific scene or interview length before committing to a battery count.