A power bank is a rechargeable battery pack that stores energy and later charges phones, tablets, and headphones.
Portable batteries took off once phones started doing everything. A small pack in your bag means you’re not guessing whether maps will make it to the end of the day. Below you’ll get the plain-English meaning, how the tech works, what the specs actually tell you, and how to pick the right pack.
Power Bank Meaning And Core Parts
At its core, a portable charger is one or more lithium cells, a charge controller, and a DC-DC converter wrapped in a shell. The controller pulls power from a wall charger or USB port to refill the cells. The converter then boosts that stored energy to the right voltage for your gadget over USB-A or USB-C.
How It Works In Practice
You plug the pack into the wall to fill its cells. Later, you plug your phone into the pack. The electronics negotiate a safe voltage and current, then feed your device while monitoring heat and shutdown conditions. Many models also pass through power, so the pack can charge while it tops up your device.
Capacity: mAh, Wh, And Real-World Meaning
Two numbers matter: milliamp-hours (mAh) and watt-hours (Wh). mAh describes electric charge; Wh expresses actual energy. To compare packs fairly, convert mAh to Wh using Wh = mAh × V ÷ 1000, and use 3.7 V for typical lithium cells. That makes a 10,000 mAh pack about 37 Wh.
| Rated Capacity | Approx. Energy (Wh) | Typical Use |
|---|---|---|
| 5,000 mAh | ~18.5 Wh | One light phone refill; pocket carry |
| 10,000 mAh | ~37 Wh | Two phone refills; earbuds and watch too |
| 20,000 mAh | ~74 Wh | Phone and tablet recharges; long travel days |
| 27,000 mAh | ~100 Wh | Maximum most airlines allow without approval |
Charging Speeds And Standards
USB-C changed the game. With USB Power Delivery, chargers and devices can request higher voltages like 9 V, 15 V, 20 V and beyond, enabling fast charging for phones and many laptops. Some packs also offer PPS, which fine-tunes voltage in small steps for cooler, efficient charging.
Want the spec source? See the USB-IF page on USB Power Delivery for the official overview of voltage options and the 240 W ceiling.
Common Types You’ll See
Slim daily carry: 5,000–10,000 mAh for phones and earbuds.
Travel all-rounders: 10,000–20,000 mAh for phones and tablets.
Laptop-capable bricks: 20,000–27,000 mAh with 45–140 W USB-C output.
Solar-assisted units: integrated panels to trickle charge outdoors.
Key Features That Matter
Ports: A mix of USB-C for input/output and USB-A for legacy cables keeps things flexible.
Output power: Look for 20–30 W for phones, 45–65 W for light laptops, and 100 W+ for power-hungry rigs.
Safety: Over-temperature, over-current, and short-circuit protection are a must. Third-party safety marks add confidence. UL 2056 is the dedicated safety standard for these products.
Display: A clear percent readout beats vague four-LED bars.
Pass-through: Handy on a desk, less useful on the go.
What A Given Capacity Can Do
A midrange phone battery is roughly 11–15 Wh. A 37 Wh pack can refill it two to three times accounting for conversion losses. A handheld console sits closer to 16–20 Wh per charge, so expect one to two full refills from the same pack.
Airline Rules You Should Know
Packs with lithium cells ride in carry-on bags. Airlines and regulators treat them as spare batteries. Typical limits allow up to 100 Wh without approval; 101–160 Wh may fly with airline permission; larger units don’t go on passenger planes. Terminals must be protected from short circuit. Check the TSA page for power banks and IATA’s passenger guidance for the global view.
Safety Standards And Build Quality
Look for enclosures that don’t rattle, smooth seams, and ports that feel secure. Brands that test against recognized standards add a layer of assurance. UL describes its UL 2056 program, which targets fire, explosion, and abuse testing specific to portable packs.
Care, Charging Habits, And Lifespan
Lithium cells prefer shallow cycles. Topping up between 20% and 80% helps. Stash the pack around half full if it’ll sit for months. Heat is the enemy, so don’t bake it in a car or under a pillow.
Troubleshooting Common Problems
Pack won’t start charging: tap the power button, then try a known-good cable. Some ports sleep until they see a load.
Phone charges slowly: pick the USB-C PD port and a cable rated for the wattage. Disable battery-saving modes while topping up.
Pack stops early: high-draw devices can trigger protection. Try a different port or step down the load.
Estimating Real-World Run Time
Multiply the pack’s Wh by 0.7 to account for conversion losses and cable heat. Divide that by your device’s Wh to get expected full charges. The 0.7 rule isn’t perfect, yet it gives you a quick yardstick across brands.
Buying Checklist
Capacity in Wh that fits your day.
USB-C PD output that matches your device’s adapter rating.
Two or more ports so you’re not choosing which gadget lives.
Verified safety testing and a clear warranty.
A weight and footprint you’ll actually carry.
When A Bigger Pack Makes Sense
If you shoot video on the go, run a handheld gaming session, or need a laptop cushion for meetings, a 20,000 mAh class unit earns its space. Commuters and light travelers can save weight with 10,000 mAh and a fast 30 W USB-C output.
When You Need Laptop-Level Output
Ultrabooks sip 30–65 W; workstations draw more. A pack that supports multiple fixed PD voltages—5, 9, 15, 20 V—covers most notebooks. Newer extended ranges go well past 20 V for high-watt gear, but check your device’s label and the cable rating before buying.
Why Some Packs Heat Up
Fast charging pushes higher current or voltage, which creates heat in cells, converters, and cables. Good designs spread and shed that heat. If your pack feels hot to the touch, give it air, lower the load, or switch to a slower profile.
Recycling And End Of Life
Don’t toss a spent pack in the trash. Many cities accept lithium packs at e-waste depots or retailer take-back bins. Tape the terminals before transport to prevent shorts.
Reading A Spec Sheet Without Guesswork
Battery rating: Brands often print the cell rating in mAh at 3.7 V. That isn’t the same as output capacity at 5 V or 9 V. Expect losses during conversion.
Output lines: You’ll see entries like “USB-C1: 5 V 3 A, 9 V 3 A, 15 V 3 A, 20 V 5 A.” The last number times the voltage gives watts. In that example, the peak is 100 W on the C1 port.
Shared power: Multi-port models sometimes share one power budget. If two devices draw hard, each port may drop to a lower profile.
Refill speed: Input specs tell you how fast the pack itself recharges. A pack that accepts 45–65 W cuts downtime a lot if you own a capable wall charger.
Travel Tips That Prevent Hassles
Carry-on only: Keep packs in the cabin, not in checked bags. Place them where crew can see them during use.
Mind the limit: Stay at or under 100 Wh for the smoothest screening experience. If you must bring a larger unit, contact the airline in advance.
Cover the pins: Use terminal covers or a small case so metal items can’t short the ports in your bag.
Safety Certifications And Good Signs
Third-party evaluation helps weed out risky builds. Look for listings against UL 2056 for packs and UL 62368-1 or IEC 62368-1 for chargers. A maker that publishes test reports, over-current trip points, and thermal cutoffs inspires confidence.
Cables And Accessories Matter
A weak cable can waste power and cap speeds. For USB-C, pick an e-marked cable for anything above 60 W, and keep it short when you can. For older gear, use known-good USB-A cables and toss frayed cords.
Simple Math That Helps Buyers
Use this quick method to estimate charges: take the pack’s Wh, multiply by 0.7, then divide by your device’s battery Wh. If your phone holds 12 Wh and your pack is 74 Wh, 74 × 0.7 ÷ 12 ≈ 4 full charges under ideal conditions. Real numbers vary with screen-on time and cable losses.
Care Tips For Longer Life
Keep the pack near room temperature. Cycle it monthly if it sits. Avoid full drains every time; partial cycles are easier on cells. Wipe ports free of lint so plugs seat fully. If the case swells or vents a chemical smell, stop using it and take it to a battery drop-off as soon as possible.
Choosing The Right Size For Daily Carry
Match capacity to your longest stretch away from outlets. City commuters often do fine with 10,000 mAh. Students and travelers who stream video or game on the go lean toward 20,000 mAh. Creators who shoot on mirrorless cameras, action cams, or phones with gimbals benefit from packs that can push 45–65 W over USB-C.
Why Wh Labeling Matters At Airports
Security staff measure risk by stored energy. A clear Wh label speeds screening and aligns with airline policy. If your unit only lists mAh, multiply by 3.7 and divide by 1000 to get Wh. Write that value on a small label near the ports.
Connector And Output Cheat Sheet
| Port Or Mode | Usual Power | Good For |
|---|---|---|
| USB-A (5 V) | 12–18 W | Older phones, earbuds, fitness bands |
| USB-C PD | 20–100 W | Modern phones, tablets, many laptops |
| USB-C PD EPR | 140–240 W | High-watt laptops and docks |