A 10,400mAh bank typically delivers ~23–28Wh to devices, giving about 1–2 phone charges or several hours of low-watt use.
If you’re weighing a 10,400-mAh portable charger, you want a clear answer up front. The cell inside stores roughly 38.5Wh (based on a 3.7V lithium pack). After conversion to 5V and the losses in the boost circuit, usable energy lands closer to the mid-20s in watt-hours. That translates to one to two full phone refills, or a few hours of steady power for small electronics, depending on load and how you use the device while charging.
Quick Estimates You Can Trust
Here’s a fast way to set expectations. Numbers below assume typical real-world efficiency in the 60–75% band and modern phone and tablet battery sizes. Actual results vary with screen time, apps, and charging speed.
| Device Type | Typical Battery (Wh) | Expected From 10,400-mAh Bank |
|---|---|---|
| Compact Phone | 10–12Wh | ~2 charges (screen mostly off) |
| Mainstream Phone | 12–14Wh | ~1.6–2 charges |
| Large Phone / Gaming Phone | 16–19Wh | ~1.2–1.6 charges |
| Small Tablet | 20–28Wh | ~0.8–1.2 charges |
| Wireless Earbuds Case | 0.3–0.6Wh | Dozens of refills |
| Smartwatch | 0.2–0.5Wh | Many refills |
| Handheld Camera / Action Cam | 4–8Wh | ~3–6 refills |
Where The Runtime Number Comes From
Two facts set the baseline:
- Energy math: Watt-hours = milliamp-hours × volts ÷ 1000. Most power banks use ~3.7V cells. So 10,400mAh × 3.7V ÷ 1000 ≈ 38.5Wh. See a clear walkthrough of the mAh→Wh math in this mAh-to-Wh guide.
- Conversion losses: The pack boosts 3.7V up to USB output (5V or a USB-PD profile). That step costs energy. Major vendors note that external batteries usually deliver only ~60–70% of their rated capacity to a device, due to voltage conversion and overhead. Anker’s service note explains this plainly and uses the same math most buyers use when planning trips; see Anker’s capacity explanation.
Using those two points, a realistic usable energy range for a 10,400-mAh unit is about 23–29Wh to the device. That’s the pool you draw from, and every scenario below taps into that pool at a different rate.
Plain-English Formula And Easy Examples
Here’s a simple path you can reuse for any gadget:
- Convert bank capacity to Wh at 3.7V: 10,400 × 3.7 ÷ 1000 ≈ 38.5Wh.
- Apply real-world efficiency: pick 65% as a safe mid-case → ~25Wh usable.
- Compare that to your device’s battery in Wh to estimate charge counts or hours.
Worked examples:
- Modern phone (about 13Wh): 25Wh ÷ 13Wh ≈ ~1.9 full charges with the screen mostly off during charging.
- Large Android (19Wh): 25Wh ÷ 19Wh ≈ ~1.3 full charges.
- Small tablet (25Wh): 25Wh ÷ 25Wh ≈ ~1 full charge.
If you tend to scroll or game while tethered to the pack, your phone burns some of that 25Wh on the spot. That drops the count a bit.
Why Two Users Get Different Results
Five variables drive endurance more than the label on the box:
Cell Chemistry And Actual Voltage
Most compact banks ship with a single-cell lithium pack around 3.7V nominal. Sellers list mAh at cell voltage, not at the 5V USB output. The energy is the same, but after boosting, the current drops and heat shows up. That’s the main reason a pack with a huge mAh figure doesn’t translate one-for-one to phone refills.
Conversion Efficiency And Heat
Boost converters waste a slice of energy as heat, and the slice depends on load and temperature. Light loads and gentle charging tend to waste less energy. High-watt fast charging runs warmer and wastes more.
Charging Speed And USB-PD Profiles
USB-C and USB Power Delivery can raise voltage, which helps move power efficiently at higher wattages. That’s great for speed, but sustained high output still eats through the usable pool faster. See the official USB-PD overview for the range of supported power levels.
Phone Behavior While Charging
Screen on, GPS, gaming, video recording, and hot weather all raise draw. If your phone sips 3–5W while you scroll, part of the bank’s output goes to live use, not the battery bar. That’s why “two charges” on paper may look closer to one and a half for heavy users.
Cable Quality And Port Choice
Loose connectors or skinny cables waste energy as heat at higher currents. A short, certified USB-C cable helps reduce that waste. Ports on a bank share the same pool; splitting across two ports at once raises losses a bit.
Close Variation: 10,400-mAh Portable Charger Runtime Rules
Here’s a compact set of rules you can apply without a calculator:
- Think in Wh, not just mAh. A cell rated around 38.5Wh yields mid-20s Wh to devices in typical use.
- Phones with 12–14Wh batteries see about two refills if you charge while idle.
- Big-battery phones (16–19Wh) land near one to one-and-a-half.
- Small tablets hover near a single full refill.
- Earbuds, watches, and cameras sip so little that a bank like this lasts through many cycles.
How Fast Charging Changes The Picture
Higher watts shorten waiting time but raise losses. A 20–30W phone session can run several degrees warmer than a 10W trickle. The battery controller in your device also throttles at high state of charge, which tilts the efficiency curve. A practical tip: use fast charging when you need a top-off in a rush, then let the rate fall for the last stretch.
Realistic Phone Charge Counts
Pick a mid-case usable pool of ~25Wh and match it to common battery sizes. This gives you a repeatable yardstick across brands.
- 12–13Wh phone: ~1.8–2 refills.
- 15–16Wh phone: ~1.4–1.6 refills.
- 18–19Wh phone: ~1.2–1.4 refills.
If your phone’s spec sheet lists only mAh, convert to Wh by multiplying by the battery’s nominal voltage (often near 3.8V or 3.87V on many phones). That small voltage difference nudges results slightly.
Table Of Hours By Load (Handhelds, Routers, Lights)
Sometimes you’re not refilling a battery at all; you’re powering a gadget directly. The table below shows estimated run hours from a 10,400-mAh pack at two common usable-energy assumptions. Pick the load that matches your device’s draw.
| Device Load (W) | Hours @ ~25Wh Usable | Hours @ ~29Wh Usable |
|---|---|---|
| 2W (LTE hotspot on low) | ~12.5 h | ~14.5 h |
| 3W (Bluetooth speaker) | ~8.3 h | ~9.7 h |
| 5W (action cam / light) | ~5 h | ~5.8 h |
| 10W (phone fast-ish charge) | ~2.5 h | ~2.9 h |
| 20W (rapid phone charge) | ~1.25 h | ~1.45 h |
Common Pitfalls That Shrink Runtime
Charging While Gaming Or Filming
Live draw eats into the pool. A phone pulling 5W during a 10W charge effectively nets only half of that into the battery.
Leaving The Bank In A Hot Car
Heat raises resistance and hurts efficiency. It also ages the cell faster, which lowers capacity over time.
Thin Or Long Cables
High current across a skinny or very long cable wastes energy as heat. A short, well-made cable helps at 20W and up.
Two Devices At Once
Split charging is handy on trips. Just expect a small drop in total delivered energy due to higher average current and extra conversion overhead.
Flight Rules And Pack Size Planning
A 10,400-mAh unit sits far below airline watt-hour limits and rides in a carry-on without special permission. If you’re weighing bigger packs for laptops, look at the label in watt-hours, not just mAh, and keep it within airline limits listed by your carrier.
How To Stretch Every Watt-Hour
- Top off during downtime. Charge while the screen is off to push more energy into the phone battery instead of live use.
- Match the speed to the moment. Use high wattage for a quick lift, then let it ramp down.
- Use USB-C first. Modern USB-C ports and a solid cable trim losses at higher power.
- Keep temps moderate. Shade on a beach day helps both efficiency and long-term capacity.
- Avoid full drains. Refill the bank before it hits single digits; boost circuits often run less efficiently near empty.
Worked Scenarios For Popular Devices
Daily Commuter With A Mid-Range Phone
Screen-on time sits near two hours, with light maps and music. A mid-range phone battery around 12–13Wh pairs cleanly with a mid-20s-Wh usable pool. Expect two refills across a weekend trip if you charge while idle, or about one-and-a-half if you stream during each session.
Traveler With A Large-Battery Android
Navigation, photos, and tethering raise draw. Big batteries in the 16–19Wh bracket usually land near a single clean refill and a partial top-off. Add a second compact bank or step up to a higher-Wh pack if you also run a hotspot.
Action Camera Day
Many action-cam batteries sit between 4 and 8Wh. A 10,400-mAh bank refills those several times. Charge cells while you break for food and you’ll finish the day with spares to spare.
When A Larger Bank Makes Sense
Laptops and handheld gaming PCs often use 30–60Wh per internal battery. A compact bank won’t cover a full laptop refill, though it can extend time on light tasks. If you plan to power a handheld gaming PC at 20–30W for long stretches, pick a higher-Wh model with USB-PD support and a cable rated for the wattage you need.
Troubleshooting: Getting Less Than You Expected
- Bank stops early: Many packs cut output near low state of charge to protect the cell. That’s normal.
- Phone never hits 100%: Some devices taper hard above 80–90%. Try finishing on a slower port.
- Pack feels hot: Let it rest and reduce load. Heat robs efficiency and ages the cell.
- Old pack, lower counts: Cells lose capacity with cycles and time. If your bank is years old, the usable pool has shrunk.
Bottom Line Numbers You Can Rely On
A 10,400-mAh portable charger stores about 38.5Wh and typically delivers mid-20s Wh to your devices. That equals one to two charges for most phones, a single charge for many small tablets, and long run time for low-draw gadgets. Use the simple Wh math, set your expectation range with a 60–75% efficiency band, and you’ll plan trips with far less guesswork.