BATTERY POWER · LEVEL 3
Power banks: the backup every household should own.
A phone that dies in the first hour of an outage is a phone you cannot use to check on family, read alerts, or call for help. A good power bank is the cheapest, simplest insurance against that, and the one piece of backup power most households are still missing.
WHERE THIS RUNG FITS
A rechargeable battery with USB ports.
That is all a power bank is: a lithium battery in a case, with USB sockets to charge your small devices. It sits on the third rung of the battery capability ladder, between simple rechargeable cells and the far larger portable power stations. Knowing exactly what it can and cannot do keeps you from either overspending or expecting a pocket battery to run a refrigerator.
What it powers well
- Smartphones and tablets
- USB headlamps, flashlights, and lanterns
- A portable Wi-Fi hotspot or a handheld radio
- Bluetooth earbuds, e-readers, and small USB fans
- With USB-C Power Delivery, many laptops
What it cannot do
- Run anything with a normal wall plug
- Power a refrigerator, fan with a cord, or lamp with an AC bulb
- Drive a CPAP or other AC medical device
- Provide days of power for a whole household
- Deliver every milliamp-hour printed on the label
Those larger jobs belong to a portable power station, the next rung up.
READING THE NUMBERS
The big number on the box is not what you get.
Power banks are sold on milliamp-hours, a number chosen because it looks large. It describes the raw cells inside, not the energy that reaches your phone. Understanding the gap between the two is the single most useful thing on this page.
WHAT mAh MEASURES
Milliamp-hours count capacity at the cell's own voltage, about 3.7 volts. A 20,000 mAh bank sounds like it should charge a 4,000 mAh phone five times. It will not, because the two numbers are measured at different voltages and energy is lost in between.
WHAT Wh MEASURES
Watt-hours fold the voltage in, so they describe real stored energy. They are also the number airlines regulate. When a bank lists its watt-hour rating, that is the honest figure to judge and compare it by.
THE MATH, WORKED
watt-hours = (mAh × 3.7) ÷ 1000
A 20,000 mAh bank holds about 74 watt-hours. Charging loses 20 to 35 percent to voltage conversion and heat, so roughly 50 watt-hours actually reach your device. A typical phone battery is around 15 watt-hours, which works out to about three full phone charges from that bank, not the five the raw number implies.
The rule to carry away: expect a power bank to deliver two-thirds to three-quarters of its advertised capacity in real use. If a pocket-sized bank claims 50,000 mAh, be skeptical. The cells that would hold that much do not fit in that space.
PORTS, CABLES, AND SPEED
The port and the cable decide the speed.
Two banks with the same capacity can charge at very different speeds, and the difference is almost never the battery. It is the port standard and the cable. Here is what the labels mean.
USB-A and USB-C
USB-A is the older rectangular port. USB-C is the newer oval one, reversible and capable of much higher power. A modern bank should have at least one USB-C port, since that is what fast charging and laptop charging run through.
Power Delivery and quick charge
USB-C Power Delivery lets the device and bank agree on higher, safe power levels, up to 100 watts or more. Various quick-charge standards do something similar. For fast phone charging or topping a laptop, look for a stated PD wattage rather than a vague fast label.
Input versus output
Output is how fast the bank charges your device. Input is how fast the bank itself refills. A slow input rating means an empty bank takes all night to recharge, which matters when you are cycling it during a multi-day outage.
The cable is often the bottleneck
A cheap or old cable can cap charging speed no matter how capable the bank and phone are. High-wattage charging needs a cable rated for it. Keep a good USB-C cable with the bank, and treat the cable as part of the kit, not an afterthought.
Pass-through charging
Some banks can charge a device while being charged themselves. It is convenient, but it heats the battery because it is charging and discharging at once, and not every bank supports it well. For daily use, fill the bank, then unplug it and use it. Save pass-through for banks rated for it.
MATCH IT TO THE TRIP, NOT THE SPEC SHEET
Choosing the right size.
Bigger is not better here. A bank you will not carry because it is heavy does nothing. Match the size to how you will actually use it, and let the airline watt-hour limit set the ceiling if you fly.
| Use | Rough capacity | What it does |
|---|---|---|
| Pocket, everyday | 5,000–10,000 mAh | One to two phone top-ups. Slips in a pocket or purse for a single day. |
| Day trip and travel | 20,000 mAh (~74 Wh) | Three to four phone charges. The sweet spot for most people, and airline-friendly. |
| Multi-day outage | 25,000–27,000 mAh (~100 Wh) | Keeps two phones and a headlamp going for days of rationed use. Right at the airline ceiling. |
| Laptop-capable | 20,000 mAh+ with USB-C PD, 60–100 W out | Tops a laptop as well as phones. Look at output wattage, not just capacity. |
A practical household plan: one 20,000 mAh bank per two people, kept charged, with a second bank as a buffer in case one is low when an outage starts. That covers communication through nearly any short outage and buys real time in a long one.
SAFETY AND FLYING
Small battery, real rules.
A power bank holds a lot of energy in a small space, which is exactly why airlines regulate it and why a damaged one deserves respect. The travel rules below come from the Federal Aviation Administration.
Flying with a power bank
- Carry-on only, never checked. The FAA requires spare lithium batteries and power banks to travel in the cabin with you, not in checked baggage.[1]
- Watch the watt-hours. Up to 100 Wh needs no approval. From 101 to 160 Wh you need airline approval and may carry at most two. Over 160 Wh is forbidden.[2] Most consumer banks sit under 100 Wh, which is roughly 27,000 mAh.
- If your bag is gate-checked, take the power bank out and keep it with you in the cabin. Protect the terminals from short circuit.[1]
- Tell the crew right away if a battery or device starts overheating, swelling, smoking, or burning. Cabin crews are trained for exactly this.[1]
- Check your airline. Through 2026 several carriers added stricter rules of their own, such as keeping power banks out of overhead bins and not charging them during the flight. The FAA rules are the floor; your airline can be tighter.[2]
Stop if it swells or heats
A bank that puffs up, grows hot rather than warm, smells sharp, or hisses is failing. Stop using it, move it to a hard nonflammable surface away from anything that burns, and retire it.[3]
Beware counterfeit capacity
No-name banks routinely claim capacities the cells cannot physically hold, and often skip the protection circuitry a real bank carries. Buy from the maker or an authorized seller.[4]
Charge on a hard surface
Never charge a bank on a bed, couch, or under a pillow where heat cannot escape. Use a quality cable and charger, and unplug it once it is full.
Keep it out of the hot car
Heat ages a lithium battery quickly and raises its fire risk. A closed car in summer is one of the worst places to store one. Bring it inside.
Protect the terminals
Loose in a bag with keys and coins, a charging port and metal can short. Keep the bank in a pocket or sleeve of its own, not rattling around with metal.
Recycle a dead one
A worn-out bank is a lithium battery and must never go in household trash or curbside recycling. Take it to a battery collection site or hazardous waste facility.[5]
KEEPING IT READY
A dead bank in a drawer helps no one.
The whole value of a power bank is that it is charged and findable when the lights go out. Four small habits keep it that way.
Top it up on a schedule
Power banks slowly lose charge sitting idle. Charge fully, then top up every three months whether you have used it or not. For long-term storage without rotation, leaving it around half to two-thirds full is easiest on the cells.
Store the cable with the bank
A USB-C bank with no USB-C cable is a paperweight in an outage. Tape or band the right cable to each bank so they never get separated.
Test it now and then
Once or twice a year, actually charge a phone from it. You confirm it still works and learn how many real charges it delivers, which tells you when it is fading.
Know when to replace it
Retire a bank that swells, runs hot, or holds noticeably less than it used to. Heavy daily use wears cells in a few years. A fading bank you are counting on is worse than no bank.
WHAT GOES WRONG
Five easy mistakes.
Buying on mAh alone. The headline number ignores conversion losses and says nothing about charging speed. Read the watt-hours and the output wattage too.
Letting it sit dead. A bank you never top up is empty exactly when you need it. Put it on the same quarterly reminder as your smoke alarm checks.
No cable with it. The most common outage failure. Keep the matching cable attached to the bank.
Trusting a suspicious deal. A tiny bank claiming enormous capacity for a few dollars is claiming something the physics does not allow. Cheap and honest is fine; cheap and impossible is a fire risk.
Expecting AC power. A power bank has USB ports, not wall outlets. If you need to run something with a plug, you have moved to the power station rung.
WHERE TO GO NEXT
Keep climbing.
The Battery Power guide
The full five-level ladder, from disposable cells to whole-home backup.
Portable power stations
Level 4: real wall outlets for CPAPs, fans, lighting, and small refrigeration.
Disposable batteries
Level 1: the cells that run flashlights, radios, and smoke alarms.
Power Needs Calculator
Total your loads to see when you have outgrown a bank and need a station.
SOURCES
- Federal Aviation Administration, PackSafe, "Lithium Batteries." faa.gov/hazmat/packsafe/lithium-batteries. Accessed 16 September 2026.
- Federal Aviation Administration, PackSafe, "Airline Passengers and Batteries," and the FAA spare-battery packing poster. faa.gov/hazmat/packsafe/airline-passengers-and-batteries. Accessed 16 September 2026.
- U.S. Consumer Product Safety Commission, "Batteries" hazard and voluntary-standards guidance. cpsc.gov. Accessed 16 September 2026.
- U.S. Consumer Product Safety Commission, consumer safety warning on unprotected lithium-ion cells, 2021. cpsc.gov. Accessed 16 September 2026.
- U.S. Environmental Protection Agency, "Used Lithium-Ion Batteries." epa.gov/recycle/used-lithium-ion-batteries. Accessed 16 September 2026.