Short answer: estimating how long an NP-F pack lasts needs one formula — runtime in hours ≈ battery Wh × 0.85 ÷ device wattage. The 0.85 accounts for conversion losses in step-up and step-down regulation, and Wh = nominal 7.2V × capacity in Ah. An F970, for example, is 7.2V × 6.6Ah = 47.5Wh; driving an 8W monitor, 47.5 × 0.85 ÷ 8 comes to about 5 hours. Learn the formula and you can work out any device yourself instead of guessing.
1. First, convert mAh to Wh
The 6600mAh printed on a pack describes charge, not energy. At the same 6600mAh, a 7.2V battery holds twice the energy of a 3.6V one. Any comparison across devices has to be made in Wh.
The conversion is simple: Wh = voltage (V) × capacity (Ah), where Ah = mAh ÷ 1000. Every NP-F pack is 7.2V, so you just divide the capacity by 1000 and multiply by 7.2.
| Model | Nominal capacity | Voltage | Energy (Wh) |
|---|---|---|---|
| NP-F550 | About 2200mAh | 7.2V | About 15.8Wh |
| NP-F570 | About 2600mAh | 7.2V | About 18.7Wh |
| NP-F750 | About 4200mAh | 7.2V | About 30.2Wh |
| NP-F770 | About 5000mAh | 7.2V | About 36Wh |
| NP-F960 | About 5600mAh | 7.2V | About 40Wh |
| NP-F970 | 6600mAh | 7.2V | About 47.5Wh |
One useful reference point: civil aviation allows lithium batteries up to 100Wh in carry-on without declaration, and the F970’s 47.5Wh is barely half of that, so carrying two or three is comfortably within the rules. For the declaration thresholds and quantity limits, see the rules for flying with lithium batteries.
2. Second, confirm what the device actually draws
The usual mistake in runtime estimates is not the formula but the wattage you put into it. Manufacturers’ “maximum power” and “typical draw” often differ by a factor of two. The ranges below are real-world starting points.
| Device type | Typical draw | Notes |
|---|---|---|
| 5-inch monitor (400-500nit) | About 4-6W | Moderate brightness, no internal recording |
| 7-inch high-bright monitor (1000nit+) | About 8-12W | The bright panel is the main load |
| Wireless video receiver | About 3-5W | Add to the monitor figure |
| Small LED panel | About 10-20W | Varies with brightness setting |
| High-output LED spotlight | About 25-40W | At full power, close to the pack’s output ceiling |
When no rating is given, there is a rough workaround: take the input current from the manual and multiply by the voltage. A 12V / 0.7A rating works out to about 8.4W. If the manual only says “NP-F970 recommended”, that usually means the draw is mid-to-high and a small pack will hit low-voltage cutoff quickly.
3. Third, run the numbers into a schedule
Feed the first two steps into the formula. The table below already applies the 0.85 efficiency, so it can be used directly for planning.
| Device draw | F550 (15.8Wh) | F750 (30.2Wh) | F970 (47.5Wh) |
|---|---|---|---|
| 5W monitor | About 2.7 hours | About 5.1 hours | About 8.1 hours |
| 8W monitor | About 1.7 hours | About 3.2 hours | About 5.0 hours |
| 15W panel light | About 0.9 hours | About 1.7 hours | About 2.7 hours |
| 30W spotlight | About 0.4 hours | About 0.9 hours | About 1.3 hours |
When scheduling, take another 20% off the result. The reasons are in the next section. In other words, an F970 running an 8W monitor should be planned at 4 hours, not 5.
- List every load: if a monitor, a video transmitter and a follow-focus share one pack through a D-tap or splitter, add the wattages together.
- Calculate at the highest setting: light output gets adjusted, but the schedule has to assume the brightest setting you might use.
- Convert to hours per pack: write the result on a label on the battery so nobody recalculates on set.
- Size the count to the day: total hours ÷ hours per pack, round up, then add one spare.
4. Four things that throw the estimate off
The formula gives a theoretical figure, and reality always drifts. Knowing where the drift comes from lets you build in margin ahead of time.
- Inflated capacity claims: a cheap pack labelled 8000mAh in the same shell as an F970 usually delivers around 5000mAh. Volume sets a physical ceiling on the cells, and labels beyond common sense are not credible.
- Cold: usable capacity drops noticeably below 0°C, and at -10°C it may be only 60-70% of room-temperature figures. On winter shoots, keep packs in an inside pocket and fit them only when needed.
- Voltage sag at the end of discharge: a lithium pack’s voltage falls quickly over the last 10%, and many devices trip low-voltage protection early, so usable capacity ends up below the nominal rating.
- Conversion losses rise with current: efficiency drops below 0.85 at high current; when powering a 30W device, 0.8 is closer to reality.
There is one more point that often gets missed: for LED lights, continuous discharge capability matters more than capacity. Small packs sag badly under high current, which produces the “40% left but the light will not strike” situation. That is exactly why high-output lights are generally paired with an F970 rather than an F550.
If what you need is long-term power for a mirrorless body rather than for monitors and lights, the approach is different: the body’s compartment uses a dedicated adapter, which means a dummy battery setup — see NP-FZ100 dummy battery power for the form it takes. YO’s NP-F range is conservative about capacity figures, so the calculated times generally match real use, which suits anyone scheduling by these methods. For more on the model tiers, see the NP-F960 / F970 category page.
FAQ
Why can’t I compare runtime using mAh?
Because mAh measures charge only and ignores voltage. A 7.2V 6600mAh pack holds twice the energy of a 3.6V 6600mAh pack. Only after conversion to Wh are packs at different voltages comparable.
What is the 0.85 in the formula?
It is conversion loss. The pack outputs 7.2V while the device may step up to 12V or regulate down to 5V internally, and part of the energy becomes heat along the way. Most devices land between 0.8 and 0.9, so 0.85 is a reasonable general compromise.
Why does the monitor’s remaining-time reading differ from my calculation?
Most monitors estimate remaining charge from voltage, and a lithium pack’s discharge curve is very flat through the middle, so the error is large. The display shows an approximate ratio for the current voltage, not true remaining energy. Timing by the clock is more reliable than watching a percentage.
Can two packs in parallel extend runtime?
Yes, with conditions. Parallel operation requires closely matched voltage and internal resistance; mixing old and new packs causes uneven current sharing, and the weaker pack drags the pair down. Proper dual-battery plates usually include isolation circuitry, which a plain splitter does not.