What has to line up for it to work
Two things decide whether a power bank can charge your laptop, and both have to be true. The first is the laptop's own charging port: it has to take its power over USB-C, the same reversible connector a phone uses, rather than through a round barrel plug. The second is what the bank's USB-C port can actually deliver.
That second part is USB-C Power Delivery, usually shortened to PD. It's the handshake that lets a charger and a device agree on a higher voltage, and it's what carries the wattage a laptop needs. Anker's UK guide is plain about it: a bank works "as long as the power bank supports USB-C Power Delivery (PD) and matches your laptop's power requirements". A bank that only does basic USB output can't have that conversation, so it never ramps up to laptop wattage.
The wattage your laptop asks for
A laptop draws much more power than a phone, and the figure it wants sets the whole decision. Anker's guide puts the range from "30W (20V/1.5A)" for "something like a MacBook Air" at the low end up to "100W (20V/5A) to power up quickly and efficiently" for high-performance machines.
Apple's own MacBook Air specs back up the low end. Apple lists a 30W minimum for the 13-inch Air and 35W for the 15-inch, and says both are "fast-charge capable with 70W or higher USB PD power source". So even a thin, light laptop wants around 30W to charge at all, and more to charge quickly, while a larger, high-performance machine sits nearer the 100W end. The number you actually need is the wattage printed on your laptop's own charger, and the bank has to meet or beat it.
Why a phone power bank stalls a laptop
Most people come unstuck the same way. They already own a power bank, so they assume it will do the job. Usually it won't. Anker's guide spells out why: "Most older power banks only support basic USB output, typically 5V/2A (10W) or maybe 9V/2A (18W). That's fine for phones, but not nearly enough to power up a laptop."
Line the two numbers up and the shortfall speaks for itself. A phone bank offering 10W to 18W is being asked to feed a laptop that wants at least 30W, or closer to 100W to fill up properly. At best the laptop charges painfully slowly, or only tops up while it's asleep; at worst the port does nothing at all, because the bank can't deliver the wattage the laptop insists on before it will accept a charge.
How to read the label before you buy
You can tell a laptop-capable bank from a phone bank on the box, without measuring anything. Look for two things. First, "USB-C Power Delivery" or "USB-C PD" named on the port, not just "USB-C output", which on a cheap bank can still be a trickle. Second, a wattage figure on that PD port that is at least as high as your laptop's charger, so 30W or more for a slim laptop and closer to 100W for a large one.
Capacity is the second question, not the first, but it matters. A laptop battery is far bigger than a phone's, so a small bank will barely move the needle. Anker's guide suggests starting at "20,000mAh or more" for a laptop, which is the size most laptop-capable banks are built around.
When a power bank can't help
Not every laptop can be charged this way, so check your own port first. If your laptop still charges through a round barrel plug rather than a USB-C port, an ordinary power bank has nowhere to plug in. Anker's guide is clear on the fix: "You'll need a power bank designed specifically with an AC outlet or a DC barrel output that matches your laptop's voltage." Those exist, but they're a heavier, bulkier, separate class of product, closer to a portable mains socket than to a pocket bank, so it helps to know that going in.
Which bank actually works
Once you know your laptop takes USB-C and you know its wattage, the shopping gets simple: match the bank's PD output to that number, then choose on capacity and build. Our best power banks for laptops guide is the shortlist that clears this bar, chosen on PD wattage first. If you mostly want one high-capacity all-rounder, our 20,000mAh power bank guide covers the same wattage question at that size. Travelling is the other big reason to charge on the move, and our power banks for long flights guide adds the in-seat and airline side of it.
FAQ
Q: Can any power bank charge a laptop? A: No. It needs a USB-C Power Delivery output at or above your laptop's wattage, which is usually 30W or more. Most phone power banks only manage 10W to 18W, which isn't enough to charge a laptop properly, and some won't charge it at all.
Q: How many watts do I need to charge a laptop? A: Match the wattage on your laptop's own charger. Anker's UK guide spans about 30W for a small laptop like a MacBook Air up to 100W for a high-performance machine, and Apple lists a 30W minimum for the 13-inch MacBook Air. Meeting that number lets it charge; beating it lets it charge faster.
Q: My laptop charges with a round plug, not USB-C. Can I still use a power bank? A: Not an ordinary one. A normal power bank charges a laptop over USB-C, so a laptop with a barrel-style port needs a bank with a built-in mains socket or a matching DC output. Those are larger and heavier, so check your laptop's port before buying.