How to Choose a Power Bank

Start with the job, not the spec sheet

Every power bank is a compromise between three things you cannot all maximize at once:

• Capacity: how many charges it holds (measured in mAh, better compared in watt-hours).
• Output: how fast it charges, and whether it can feed a laptop (measured in watts).
• Portability: weight and pocketability.

Push any one up and another comes down. A 24,000mAh, 140W brick is heavy; a pocketable 10,000mAh pack can’t charge a laptop. No pack wins all three, and the marketing is built to make you forget that. Name your job first; the rest of this guide tells you which spec to prioritize for it.

Capacity: how much you actually need

The single most common mistake is overbuying capacity. More mAh always means more weight and more cost, and most people carry far more than they use.

• 10,000mAh: roughly a day and a half of phone insurance. Pocketable. The right size for phone-only buyers.
• 20,000mAh: multi-day phone use, tablet top-ups, or a partial laptop charge. The all-rounder.
• 24,000mAh and up: laptop charging and the upper limit of carry-on-friendly. Heavy. Only if you genuinely charge a laptop.

One reality check holds across every brand: delivered capacity is always less than the printed mAh. Converting the battery’s internal voltage up to USB voltage loses energy as heat, so a 10,000mAh pack hands over roughly 6,000–7,000mAh in practice. That’s physics, not deception. Plan around 60–70 percent of the headline figure.

mAh vs. watt-hours: the comparison that works

Brands advertise mAh because the number looks big. But mAh measures capacity at the battery’s internal voltage (typically 3.7V), so it isn’t directly comparable across designs. Watt-hours is the apples-to-apples figure: mAh times voltage, divided by 1,000. At 3.7V, a 20,000mAh pack is about 74Wh.

Watt-hours is also what airlines regulate, which makes it the most useful number when shopping. If two packs list the same mAh but you can find their Wh ratings, the Wh figures tell you which one stores more energy.

Output: speed and whether it can charge a laptop

Output, measured in watts, decides two things: how fast a device charges, and whether the pack can charge a laptop at all.

• Up to ~22.5W: fast for phones, fine for small tablets, too slow for laptops.
• 30–65W: comfortable for tablets and entry-level laptop top-ups.
• 100W and up: full-speed laptop charging, often across multiple devices.

The trap here mirrors capacity: buying too much output. Phones rarely draw more than 25–30W even at peak, so a 100W pack charges a phone no faster than a 30W one. If you’ll never plug in a laptop, output above ~30W is money and weight spent on nothing.

One more wrinkle: a pack’s total output is shared across its ports. A 100W bank feeding two devices doesn’t give each 100W; it splits the budget. To fast-charge several hungry devices at once you want a high total rating and enough ports, which is where our top picks land.

USB-C Power Delivery: the baseline

If you buy one thing right, buy USB-C Power Delivery (PD). It’s the standard that lets a single port negotiate the correct voltage for a phone, tablet, or laptop, which is what makes a modern pack flexible enough to replace your tangle of chargers. An older USB-A-only pack can’t drive a laptop or deliver the higher voltages newer phones use. Treat a USB-C PD port as a baseline requirement in any pack you buy today.

Airline rules, briefly

Lithium batteries fly in carry-on only, never checked luggage. Anything under 100 watt-hours (essentially every consumer pack up to around 26,000mAh) needs no special approval. Keep it accessible, since some security lines ask to see it. This is the ceiling that caps how large a travel power bank can sensibly be.

Longevity: getting years, not months

Lithium cells wear with use. Most packs hold up well for a few hundred full charge cycles, then taper. Three habits stretch that:

1. Store it around half-charged when it’ll sit unused for weeks. That’s gentler than leaving it full or empty.
2. Keep it out of heat. A hot car is the fastest way to age a battery.
3. Retire a swollen pack immediately. A bulging case is a safety signal, not a cosmetic one.

Now go pick one

Once you’ve named your job and read the specs, the choice gets easy. Our Best Portable Power Banks guide maps each job to a pick: the laptop-charging Anker 737 and Baseus Blade, a phone-only budget choice, and an all-in-one for travelers. The rule that protects you from overpaying never changes: buy for the job you have, not the spec that sounds biggest. For the standards behind our recommendations, see how we test.