Short answer: for light to moderate shooting in a day, a 10000mAh power bank is enough; for heavy shooting or when you also need to top up a phone, 20000mAh is the safer choice. That conclusion comes from watt-hours rather than milliamp-hours. An LP-E17 at 1050mAh holds about 7.56Wh, while a power bank’s milliamp-hour rating is measured at 3.7V and the energy passes through two boost stages, so what actually reaches the battery is usually around sixty percent of the nominal figure. A 10000mAh bank therefore gives roughly two to three charges, not a simple division of capacities.
Why you cannot just divide milliamp-hours
A power bank rated 10000mAh is specified at a cell voltage of 3.7V, which comes to 37Wh of energy. The LP-E17 runs a 7.2V system, and 1050mAh corresponds to about 7.56Wh. On the numbers alone, 10000 divided by 1050 is about 9.5, which sounds promising, but that calculation ignores the difference in voltage.
The correct comparison is watt-hours to watt-hours: 37 divided by 7.56, about 4.9 in theory. That figure is still optimistic, because two losses sit in between.
The first is the bank boosting 3.7V to a 5V output, typically around ninety percent efficient before you count voltage drop in the cable and connector. The second is the battery boosting 5V up to 8.4V to charge its two series cells, which loses more. Stack the two, add cable heating and the constant-voltage tail of the charge, and overall efficiency commonly lands between fifty-five and seventy percent.
At sixty percent, 37Wh delivers about 22Wh into the battery, and 22 divided by 7.56 is roughly three. That is where two to three charges from 10000mAh comes from.
Rough charge counts by capacity
The table assumes sixty percent efficiency; real results vary with bank quality, cable, and temperature. The counts refer to filling a completely drained 1050mAh pack. If your pack is 750mAh, add thirty to forty percent to the counts.
| Power bank rating | Energy (approx.) | Full charges of 1050mAh | Best for |
|---|---|---|---|
| 5000mAh | 18.5Wh | About 1-1.5 | Half-day outings, one top-up |
| 10000mAh | 37Wh | About 2-3 | A day of light to moderate shooting, plus a phone |
| 20000mAh | 74Wh | About 5-6 | Two or three days out, or heavy bursts |
| 27000mAh | About 100Wh | About 7-8 | Multiple bodies and packs, team trips |
Note the airline rules: lithium batteries carried in the cabin normally must not exceed 100Wh, anything above needs carrier approval, and they are not permitted in checked baggage at all. The 27000mAh tier sits right at that line, so confirm you actually need it before buying.
Work back from your shooting volume, not from a guess about days
- Count how many packs a day actually consumes. Recall the last outing and count in packs, not frames.
- Subtract the packs you carry. If a day uses three and you carry two, the shortfall is one.
- Multiply the shortfall by 1.5. That is your safety factor, covering cold, lower efficiency, and the bank’s own aging.
- Look the number up in the table. A shortfall of one points to 5000-10000mAh; two points to 10000-20000mAh.
- If you also need to top up a phone, a microphone, or a monitor, add their watt-hours and move up a tier.
The benefit of this method is that it turns “I don’t think this will be enough” into a number you can check. Plenty of people buy 20000mAh and use a fraction of it, while others set out with 5000mAh and run dry by noon. The difference is whether they counted first.
Factors that reduce the real count
Temperature comes first. Outdoors in winter the bank’s own output falls and a cold battery will not accept much charge, so the energy that actually gets in may be only sixty or seventy percent of the room-temperature figure. Below freezing, keep the bank warm against your body rather than in an outer pocket.
Charging while shooting is second. If you charge a pack while still shooting, the load offsets part of the input and you may even lose ground. The right approach is to charge the pack you have pulled, off the camera, while the one in the body does the work.
Inflated ratings and aging in the bank are third. Products sold as 10000mAh vary widely in usable capacity, and capacity falls further after a year or two. When choosing, look at rated energy and supported output protocols rather than the milliamp-hour headline.
One more: some power banks go to sleep on low-current loads. Direct charging a battery draws little, which can fall into that window, and the symptom is a disconnect a few seconds after plugging in. Choose a model with a low-current mode or a wake button.
The T series decouples replenishment from the wall socket, and the price is accepting this arithmetic. If you are still deciding whether direct charging suits you, start with the scenarios in the T series category, then confirm fitment in the capacity and compatibility guide.
FAQ
How many LP-E17 packs can a 10000mAh bank fill?
About two to three for the 1050mAh tier, and about three to four for the 750mAh tier. Temperature, cable, and bank efficiency all affect it; in winter expect sixty or seventy percent of the room-temperature figure.
Why is the result so far from dividing the two capacities?
Because the voltages differ. The bank is rated at 3.7V and the battery is a 7.2V system, and energy passes two boost stages, each with losses. You have to convert to watt-hours before comparing, or the milliamp-hour figure will mislead you.
Can a power bank power the camera directly?
The T series charges the battery, not the camera. Charging while shooting depends on whether the body supports the relevant USB power protocol, and most bodies restrict burst or recording specifications in that state. Check the body manual.
The bank stops halfway. Why?
Most likely it entered low-current protection, or the cable has a poor connection. Try a short cable first, then a bank with a low-current mode. It can also be the battery’s own protection tripping because it is too hot or too cold.