How Many Watt-Hours Is 4,000 mAh at 24V?
A 4,000 mAh battery at 24V stores 96 Wh of energy on the cell. Watt-hours is the true measure of battery capacity because it accounts for voltage: a 5000 mAh cell at 3.7V and one at 12V store very different amounts of energy. Real-world delivered energy is typically around 81.6 Wh after conversion losses. For air travel, this battery is in the generally-allowed carry-on tier (up to 100 Wh nominal), subject to airline rules and terminal protection.
Tiers apply to nominal Wh. Spare batteries travel carry-on with terminals protected; airlines can impose stricter rules. See airline-limits section below for the full conditions.
Use this citation when referencing this page.
Formula
Wh = (mAh × V) ÷ 1000
Battery & Travel Info
FAA Airline Battery Limits
The FAA (and most international regulators under ICAO) set the following Wh ranges for lithium-ion passenger-flight battery carriage. The limits apply to the nominal 96 Wh figure, not the usable figure, so the airline checks the same number you get from the mAh × V calculation above.
| Wh Range | Typical Rule | This Battery |
|---|---|---|
| ≤ 100 Wh | Generally allowed in carry-on without airline approval | Within range |
| 100-160 Wh | Carry-on typically requires airline approval | -- |
| > 160 Wh | Generally not permitted on passenger flights | -- |
Conditions that affect how the rule applies: spare (uninstalled) lithium batteries must travel in carry-on, not checked baggage, with terminals protected against short circuits (original packaging, terminal caps, or individual plastic bags). Batteries installed in a device follow different rules than spares. Quantity limits typically permit up to two spare batteries in the 100-160 Wh range per passenger with approval, with no fixed limit on spares under 100 Wh for personal use (airlines can still restrict). Specific carriers and jurisdictions impose their own rules on top of the FAA/ICAO baseline. Check your airline's dangerous-goods page before travel; this table is a reference starting point, not a guarantee.
Device Runtime Estimates
How long will a 4,000 mAh / 96 Wh battery power common devices? Runtimes apply an 85% conversion-efficiency factor (usable energy ≈ 81.6 Wh). Device wattages below are planning figures, not measured averages for any specific model, and real runtime varies with screen brightness, CPU load, wireless radios, and ambient temperature.
| Device | Power Draw | Estimated Runtime |
|---|---|---|
| Smartphone (screen on, browsing) | 2W | 40.8 hours |
| Tablet (mixed use) | 4W | 20.4 hours |
| Ultrabook laptop (browser + docs, screen at 50%) | 15W | 5.44 hours |
| LED flashlight (medium setting) | 3W | 27.2 hours |
| Bluetooth speaker (medium volume) | 1.5W | 54.4 hours |
Estimates assume 85% conversion efficiency. Actual runtime varies with temperature, battery age, and usage patterns.
Charging Time
Time to fully charge 96 Wh at each common charger rating, assuming about 85% charging efficiency (heat losses in the charger IC and the battery's internal resistance mean less than the charger's rated watts actually reach the cell). Raw math is 96 Wh ÷ (charger watts × 0.85).
| Charger | Estimated Time to Full |
|---|---|
| USB 2.0 (5W) | 22.59 hours |
| USB-C (18W) | 6.27 hours |
| Fast charge (25W) | 4.52 hours |
| USB-C PD (45W) | 2.51 hours |
Real charging rarely holds the charger's full rated wattage end-to-end. Most chargers taper as the battery approaches 80-100% (constant-current then constant-voltage phases), so actual time-to-full is often 10-25% longer than the table figure for the last 20% of charge. Treat these as ballpark planning times, not guarantees.
Same mAh, Other Voltages
| Voltage | Wh | FAA/ICAO tier |
|---|---|---|
| 3.7V | 14.8 Wh | ≤100 Wh, generally allowed carry-on |
| 7.4V | 29.6 Wh | ≤100 Wh, generally allowed carry-on |
| 11.1V | 44.4 Wh | ≤100 Wh, generally allowed carry-on |
| 12V | 48 Wh | ≤100 Wh, generally allowed carry-on |
| 14.8V | 59.2 Wh | ≤100 Wh, generally allowed carry-on |
| 24V | 96 Wh | ≤100 Wh, generally allowed carry-on |
| 48V | 192 Wh | >160 Wh, generally not permitted on passenger flights |
Tier labels mirror the FAA/ICAO baseline. Individual airlines and jurisdictions can impose stricter rules on top, and the spare-vs-installed distinction and terminal-protection requirement still apply. See the airline-limits section above for the full conditions.