A good power bank is one of the most useful things you can carry, but the numbers on the box can be misleading. Here is what to look at, in the order that matters.
1. Capacity: the mAh number is not what reaches your phone
Power banks are rated at the battery's internal voltage, while phones charge at a higher voltage through a converter. Some energy is lost as heat. In practice, expect roughly 60 to 70 percent of the printed capacity to reach your phone. A 10,000 mAh power bank typically gives about one and a half to two charges for a phone with a 4,000 to 5,000 mAh battery. A 20,000 mAh model roughly doubles that, but also doubles the weight.
- 10,000 mAh: light and pocketable, enough for a day out.
- 20,000 mAh: good for travel or several devices, but heavier.
- Above 20,000 mAh: check airline rules before flying (limits are set in watt-hours, usually 100 Wh without approval).
2. Charging speed: match your phone's standard
Fast charging only works when the power bank, cable and phone support the same standard. Most recent Android phones and iPhones use USB Power Delivery (PD) over USB-C; some brands also use their own standards. Check the output rating in watts on the USB-C port. 18 to 20 W is enough for most phones; 45 W or more helps with tablets and some laptops. A power bank that charges itself quickly (high input wattage) also saves time.
3. Ports and cables
A USB-C port that works both ways (input and output) is the most useful. A built-in cable means one less thing to forget, but if it breaks, the whole power bank is harder to use. Count how many devices you want to charge at once, and check the total output when several ports are in use, as it is usually shared.
4. Safety and build
A power bank stores a lot of energy, so buy from a known brand or seller. In India, look for the BIS registration mark on the product or box. Good units include protection against overcharging, short circuits and overheating. Avoid power banks that swell, get very hot while charging, or come with no brand or safety information.
5. Size, weight and display
If it is too heavy, you will leave it at home. Check the weight in grams against how you will carry it. A small display showing the remaining percentage is more useful than four LEDs, especially on larger capacities.
A simple way to decide
- Everyday carry: 10,000 mAh, 20 W USB-C PD, under about 250 g.
- Travel or two devices: 20,000 mAh, 20 to 45 W, two or more ports.
- Laptop charging: check your laptop's USB-C wattage and choose a power bank that meets it.
We sometimes list power bank offers on our Deals page. Check the exact model's output and weight on the retailer's page before you buy.
