A 20,000mAh power bank does not give you 20,000mAh of usable charge. Conversion loss eats roughly 30 percent, so expect around 13,000mAh in practice.

Look at wattage, not just capacity

For a modern phone you want at least 20W PD output. For a laptop, 65W or more.

Check the safety marks

Genuine units carry BSTI, CE or FCC marking and have over-charge and over-heat protection.

The cable matters as much as the bank

A high-wattage power bank charging through a cheap or damaged cable will still charge slowly. Use the cable that came with the bank, or a properly rated USB-C PD cable, to actually get the speed printed on the box.

Pass-through charging is worth checking for

Some power banks let you charge the bank itself and a connected device from the wall at the same time. If you plan to keep one permanently plugged in at your desk, confirm this feature before you buy — not every model supports it.

Flying with a power bank

Airlines generally only allow power banks in carry-on baggage, never checked luggage, and most cap them around 100Wh without special approval. Check your airline's rules before a trip, especially for anything above 20,000mAh.

Match the size to how you actually use it

A phone-only user rarely needs more than 10,000mAh. If you also charge a tablet or laptop, or travel for days without reliable power, a 20,000mAh-plus unit with laptop-rated wattage earns its extra size and weight. Buying more capacity than you'll use just means carrying dead weight. A power bank that feels warm during use is normal; one that gets hot to the touch is not, and should be stopped and unplugged.

Battery life fades with use, like any lithium battery

Expect noticeably reduced capacity after roughly 300 to 500 full charge cycles — that's normal lithium-ion behaviour, not a defect. Storing a power bank at around 50 percent charge in a cool, dry place when it's not in regular use helps it last longer.

One bank, or several smaller ones?

A single large power bank is simpler to carry and charge, but if it dies or is forgotten, you have nothing. Two smaller banks split between a bag and a desk drawer means you are rarely caught with zero backup power, at the cost of slightly more total weight.