Xiaomi Power Bank 4i 20000mAh Review: What You Actually Get Out of It
The 20,000mAh class is the workhorse of Indian power banks, and this is a representative example of it. The useful question is not what the box says but what reaches your phone.
What it is
| Capacity | 20000mAh |
|---|---|
| Output | 33W super fast charging, Power Delivery |
| Ports | Three outputs; Type-C does input and output |
| Safety | Stated 12-layer protection |
| Supports | Android, Apple, tablets, earbuds, watches |
What 20,000mAh really delivers
Not 20,000mAh. That figure is measured at the cells' own 3.7V, and USB has to deliver at 5V or higher, so a large slice disappears in conversion before any inefficiency at all. Add conversion heat, cable resistance and your phone's own charging circuit, and the working rule is:
Expect 60–70% of the printed figure
Roughly 12,000–14,000mAh reaching a device. On a 5,000mAh phone that is about two and a half full charges — not four. This is normal physics, not a defect; the full explanation is in why a 20,000mAh power bank never gives you 20,000mAh.
The two specifications worth checking
33W output with PD. This is the useful range for a phone — fast enough to matter, and Power Delivery is an open standard so it works across brands. Be aware that a phone advertising a much higher proprietary speed will charge here at PD speed instead; see fast charging standards for why.
Type-C input and output. Easy to overlook and genuinely important: it means the pack refills over the same cable you already carry, and refills quickly. A 20,000mAh pack that only takes 10W input needs most of a day to fill itself, which quietly makes it useless for back-to-back travel.
Three ports, one shared budget
As with every multi-port device, the outputs share the total. Charging a phone, earbuds and a watch simultaneously means none of them gets the peak figure. For a single device on the Type-C port you get the full rate.
Weight, and flying with it
A genuine 20,000mAh pack weighs roughly 350–400g. That is the honest cost of the energy — a pack claiming far more at far less weight is claiming something cells cannot currently do.
For air travel it must go in cabin baggage, never checked. At around 74Wh this sits comfortably inside the common 100Wh limit, but check your airline's current rules, which vary and change. More on this, and on the warning signs to watch for in any pack, in power bank safety.
Buy this if
- You want two or more phone charges away from a socket
- You travel and want to top up a phone, earbuds and a watch from one pack
- You want the pack itself to refill quickly over USB-C
Consider 10,000mAh instead if
- You need one charge, not three — half the weight, and far more likely to actually be in your bag when you need it