mAh in a power bank means milliampere-hours—the battery’s charge capacity that hints at run time, not power.
Shoppers see big numbers on portable chargers and want to know what those figures actually deliver. The label shows mAh, a capacity unit tied to current over time. That number helps you estimate how many recharges you’ll get, how long a device can sip power, and whether a bank fits airline limits. This guide strips the jargon, gives you easy math, and sets realistic expectations before you hit buy.
What mAh Means In A Portable Charger: Plain Terms
mAh stands for milliampere-hours. Think of it as the size of the battery’s “fuel tank” measured by how much current it can supply over one hour. A 10,000 mAh pack, in theory, could deliver 10,000 milliamps for one hour, or 2,000 milliamps for five hours, and so on. Real life adds losses, but the idea holds: bigger number, larger stash of charge.
Why The Same mAh Can Perform Differently
Two chargers with the same label can behave differently because capacity is rated at the cell’s native voltage, usually around 3.6–3.7 V for lithium-ion. When that energy is boosted to 5 V (USB-A) or to higher USB-C voltages, conversion losses appear. Cable quality, device draw, temperature, and age also play a part. So mAh tells you “how much,” while the electronics inside shape “how fast” and “how many times.”
Quick Reality Check On Ratings
Portable packs often advertise cell capacity. Usable output at the USB port is smaller due to conversion and heat. A rough planning range is 60–80% of the printed figure. Premium designs sit on the higher end; older or bargain models often land lower. The tables below help you plan with that in mind.
Power Bank Capacity And Real-World Use
Use this broad table to match common sizes with likely outcomes. It frames cell-side energy (at ~3.7 V), a ballpark of what reaches your phone or earbuds after losses, and typical use cases. Treat it as planning guidance, not a lab spec.
| Label Capacity (mAh) | Approx. Usable Wh* | Typical Use |
|---|---|---|
| 5,000 | 9–12 Wh | Earbuds many times; phone top-ups |
| 10,000 | 18–24 Wh | One full phone charge, maybe two |
| 15,000 | 27–36 Wh | Two solid phone charges; small tablet boost |
| 20,000 | 36–48 Wh | Two to three phone charges; small tablet once |
| 26,800 | 48–64 Wh | Weekend phone power; mid-size tablet help |
| 30,000–40,000 | 54–96 Wh | Phones for a trip; light laptop trickle if PD supports |
*Usable watt-hours after typical conversion losses; range reflects design and conditions.
mAh Vs Wh: The Two Numbers You’ll See
mAh is capacity tied to current over time. Watt-hours (Wh) combine both charge and voltage into one energy figure. Wh is the better cross-brand yardstick because it normalizes different voltages. Many airlines also reference Wh for limits, so it’s handy to know both.
The Simple Conversion
To convert cell-side capacity to energy: Wh = (mAh × V) ÷ 1000. With a 10,000 mAh pack built on 3.7 V cells, energy is about 37 Wh. If a maker quotes Wh at 5 V output, that’s a different basis; always check which voltage they used. When a product page shows both mAh and Wh, trust the Wh figure for flight rules and apples-to-apples shopping.
Why Your Phone Doesn’t See The Full Number
Energy leaves the cells, passes through a boost circuit, travels the cable, then charges your device. Every step trims a bit. Fast charging creates more heat and extra loss. Your phone also stops charging near full to protect its own battery. The outcome: usable energy is smaller than the label, and faster sessions shave a little more.
How To Estimate Real Recharges
Here’s a quick way to predict outcomes without a spreadsheet.
Step 1: Convert To Wh
Multiply the mAh by the cell voltage (usually ~3.7) and divide by 1000. A 20,000 mAh pack gives roughly 74 Wh at the cell level.
Step 2: Apply A Practical Factor
Plan on 65–75% reaching your device under mixed use. That same 20,000 mAh pack may deliver 48–56 Wh at the port across a trip.
Step 3: Compare With Your Device
- Recent phones: around 11–17 Wh batteries.
- Small tablets: around 18–30 Wh.
- Ultraportable laptops: 35–60 Wh and up.
Now divide usable Wh by your device’s Wh. If your phone is 14 Wh and your bank delivers ~52 Wh on a weekend, you might see three full charges with some left for top-ups.
Charging Speed, Ports, And The mAh Number
mAh doesn’t set speed. It sets size. Speed comes from the output profile: USB-A 5 V, USB-C Power Delivery (PD), and vendor fast standards. A pack with lower mAh can charge a phone faster than a larger pack if it supports higher PD levels. The reverse also happens: a huge pack can be slow if it only offers basic 5 V output.
PD Levels To Watch
- 18–30 W: Swift phone charging, small tablets.
- 45–65 W: Many Chromebooks, compact Windows laptops.
- 100 W+: Demanding notebooks; requires quality cable and firmware.
Match the bank’s claimed watts to your device’s input spec. If your laptop wants 65 W, aim for a pack that can hold that level on a single USB-C port, not a shared total across ports.
Travel Rules: Will This Power Bank Fly?
Airlines use watt-hours to decide what can board. Most carriers allow spare lithium-ion batteries and portable chargers in carry-on up to 100 Wh without special approval. Between 101–160 Wh, many allow up to two spares with approval. Checked baggage is off-limits for loose lithium packs. Verify your route with the latest rules before you go. See the FAA’s PackSafe lithium batteries page for thresholds and packaging guidance.
Buying Guide: Pick The Right Size For Your Use
Start with your device battery sizes and days away from outlets. Then pick a pack that meets both energy and speed needs.
Commuter And Day Trips
For calls, maps, and music, a slim 5,000–10,000 mAh bank is light and enough. If your phone supports fast USB-C, pick a model with at least 18–30 W PD.
Weekend Getaways
For photos and navigation, 15,000–20,000 mAh strikes a balance between weight and staying power. Look for dual-port output to top up a phone and earbuds at once.
Work Bag Or Student Setup
If you move between classes or meetings and carry a small laptop, 26,800–30,000 mAh with 45–65 W PD keeps you covered. Check that the bank can sustain the rated wattage on a single Type-C port.
Creators And Long Hauls
For cameras, tablets, and a heavier notebook, aim for 30,000–40,000 mAh with 65–100 W PD. Watch airline limits; a 99 Wh bank is common for travel because it fits under the 100 Wh cap while packing headroom.
Common Misreads And Marketing Traps
“Output mAh” Printed Big
Some packaging quotes mAh at 5 V output, while others quote cell-side mAh at ~3.7 V. The numbers look similar but represent different energy totals. When both are listed, rely on Wh to compare.
Total Watts Across Ports
A spec might say “65 W total” then split 45 W + 20 W across two ports. If your laptop needs the full 65 W on one cable, that pack may throttle.
“Up To X Charges” Claims
Those counts assume gentle conditions, short cables, and no background drain. Real counts go down with navigation, gaming, or cold weather.
Clear Math Examples You Can Copy
These quick cases show how to turn a label into expectations. Swap in your own numbers as needed.
| Scenario | Back-Of-Napkin Math | What To Expect |
|---|---|---|
| 10,000 mAh bank → phone | 10,000 × 3.7 ÷ 1000 ≈ 37 Wh → ~70% usable ≈ 26 Wh | About 1–2 phone charges |
| 20,000 mAh bank → phone & buds | 20,000 × 3.7 ÷ 1000 ≈ 74 Wh → ~70% usable ≈ 52 Wh | Two to three phone charges, buds many times |
| 26,800 mAh bank → small tablet | 26,800 × 3.7 ÷ 1000 ≈ 99 Wh → ~70% usable ≈ 69 Wh | Tablet once, plus phone top-ups |
| 30,000 mAh bank → compact laptop (65 W PD) | 30,000 × 3.7 ÷ 1000 ≈ 111 Wh (watch flight limits) | Meaningful top-ups; may be over most airline caps |
Cables, Heat, And Care Tips
Use The Right Cable
High-power PD needs e-marked USB-C cables rated for the wattage you plan to use. A weak cable can cap speed or drop the session.
Keep It Cool
Packs deliver better when they’re not roasting in a car or stuffed with no airflow. Heat increases loss and ages cells faster.
Top Off Smartly
Shallow discharges and partial recharges are fine for lithium-ion. Long storage? Leave it around mid charge and store in a dry place.
Specs To Scan On The Box
- Wh Figure: The best cross-brand energy number and the number airlines quote.
- Max PD Per Port: The highest sustained watts on one USB-C port.
- Total Output: Helps if you charge two devices at once.
- Input PD: Fast self-charging saves time between sessions.
- Safety Marks: Look for reliable certifications and a clear warranty.
When To Step Up Capacity
Upgrade if you often run navigation, stream during commutes, or tether a laptop. Multi-day trips off-grid or heavy camera use are also cues. If your pack often lands below 20% by evening, the next size up will smooth your day.
Trusted References You Can Check
For a clear definition of milliampere-hour and how capacity ratings work, see Battery University’s glossary entry for mAh. For flight limits and packing guidance on spare lithium batteries and portable chargers, review the FAA’s PackSafe lithium batteries guidance. Both resources align with how energy, capacity, and airline thresholds are presented in this guide.
Quick Recap You Can Act On
- mAh is the size of the charge tank; Wh is the energy yardstick.
- Convert with Wh = (mAh × 3.7) ÷ 1000 for cell-side energy.
- Plan on 60–80% reaching your device after losses.
- Match PD wattage to your phone, tablet, or laptop input needs.
- Stay under 100 Wh for carry-on ease; check airline pages when close.