Power Bank Buying Guide: From Real Capacity to Fast Charging
NTechnical team · NovaCartAugust 10, 20261 min readUpdated: September 11, 2026
Know these 5 things before buying a power bank so you don't waste your money.
Power banks can look alike on the outside, but their quality varies wildly. This guide will help you separate real specs from marketing claims.
What's the real capacity?
The number printed on the shell (e.g. 20,000mAh) is the cell capacity at 3.7V; the real output at 5V will be roughly 60–70% of that figure.
- Everyday phone use: a 10,000mAh unit is plenty
- Long trips: 20,000mAh or more
- Always-in-your-pocket companion: 5,000mAh with a built-in connector
An unbranded power bank without safety certification carries a fire risk. Always buy from a trusted store.
PD fast charging
If your phone supports Power Delivery, choose a power bank with at least a 20W USB-C PD output to multiply your charging speed.
| Ideal everyday capacity | 10000mAh |
|---|---|
| Recommended power | 20W PD |
| Portable weight | under 250g |