A dead battery when you are out and about is one of the most frustrating parts of modern life. A good power bank – also called a portable charger – solves that problem by letting you top up your phone anywhere, whether you are on a long train journey, at a festival, or simply away from a plug for the day. But walk into any shop or browse online and you will find dozens of options with confusing numbers on the box. This guide explains what actually matters so you can choose a portable charger that suits how you use your phone.
What is a power bank and how does it work?
A power bank is essentially a rechargeable battery in a pocket-sized case. You charge it up from the mains at home, then carry it with you. When your phone runs low, you plug your charging cable into the power bank instead of a wall socket. Inside is a lithium battery, much like the one in your phone, along with circuitry that manages safe charging in both directions. The better the internal components, the safer and more efficient the charging.
Capacity: what the mAh number really means
The headline figure on any power bank is its capacity, measured in milliamp-hours (mAh). A larger number means more stored energy and more charges before the power bank itself needs topping up. As a rough guide, most modern smartphones have batteries between 3,000mAh and 5,000mAh. So a 10,000mAh power bank will usually give you roughly one and a half to two full phone charges, while a 20,000mAh model can deliver three or four.
It is worth knowing that you never get the full advertised capacity in practice. Some energy is always lost to heat and voltage conversion during charging, so real-world output is typically around 60 to 70 per cent of the rated figure. That is normal and not a sign of a faulty unit. For a single day out, 10,000mAh is plenty and stays light. For weekend trips, camping or charging more than one device, 20,000mAh is a safer bet.
Charging speed and Power Delivery
Capacity tells you how much charge is stored, but wattage tells you how quickly it comes out. A basic power bank might only deliver 10W, which is slow. If you want fast charging on the go, look for a model that supports USB Power Delivery (USB-PD) and offers at least 18W to 20W. Higher-end power banks push 30W, 45W or more, which is enough to charge some laptops and tablets as well as phones. To get those speeds you also need a suitable USB-C cable, so pair your power bank with a proper fast charging cable rather than an old, thin one.
Ports and multiple devices
Think about how many devices you carry. If it is just your phone, a single USB-C port is fine. If you also travel with wireless earbuds, a smartwatch or a partner’s phone, choose a power bank with two or three ports so you can charge everything at once. Some models even include built-in cables, which saves you remembering a separate one. If charging several gadgets at home or on your desk is the real goal, a mains multi-port charger may suit you better than a battery pack.
Size, weight and everyday practicality
Bigger capacity always means more weight and bulk. A slim 10,000mAh power bank slips easily into a pocket or handbag and is ideal for daily use. A chunky 20,000mAh brick is better left in a rucksack. Be honest about how you will actually carry it – the most powerful power bank is useless if it is too heavy to bring along. For frequent flyers, remember that airlines limit the size of lithium batteries in hand luggage, and power banks must go in your carry-on, never the hold. Most everyday models are well within the limits, but always check before you fly.
Staying safe and looking after your power bank
Stick to power banks from reputable sellers with proper safety certification. Cheap, unbranded units can lack the protection circuits that prevent overheating. To keep yours healthy, avoid letting it sit fully flat for months, keep it out of direct sunlight and hot cars, and recharge it every so often if it goes unused. Treated well, a quality portable charger will last for years of trips and commutes.
Which power bank should you buy?
For most people, a 10,000mAh power bank with USB-C, Power Delivery and around 20W output hits the sweet spot of capacity, speed and portability. Choose 20,000mAh only if you regularly charge multiple devices or spend long periods away from the mains. Whatever you pick, matching it with a good cable and, at home, a solid wall charger gives you a complete setup that keeps your phone powered wherever you go. You can browse our full range of chargers and cables in the shop to build the kit that fits your day.