The mighty ZMI No.20 is the power bank I reach for every day, whether at work or on the road

ZMI No.20 power bank review

Power banks that claim to fast-charge laptops often fall short, but the ZMI No.20 delivers 100W output in a premium package. ZMI might not be a name you've heard of, but the brand is a key part of Mi (Xiaomi) and is well-known for making excellent, high-quality products. The No.20 is no exception, with a large 25,000 mAh (90 Wh) capacity, high-end components, and impressive multi-device charging capabilities. It’s one of the best power banks available, though it can sometimes be difficult to purchase in Australia and the US, and almost impossible to find in the UK. Amazon is often the best place to buy it, but keep in mind that it doesn't go on sale frequently.

I purchased this power bank personally and have used it for over two years. It remains my favourite laptop-ready power bank, thanks to its high performance, great form factor, and robust reliability.

The ZMI No.20 features two USB-C input/output ports and one USB-A port. The first USB-C port delivers up to 100W (20V, 5A), while the second is limited to 45W (20V, 2.25A) in or out. The USB-A port can also output 100W (20V, 5A) for PD-compatible devices like laptops, but only when using the included ZMI USB-A to USB-C cable. With a total power output of 210W across all ports, the No.20 has no issue fast charging multiple laptops, phones, or handheld gaming devices simultaneously. The 25,000 mAh capacity is also nearly the largest allowed while still being flight-safe.

This power bank also supports pass-through charging and functions as a UPS, ensuring uninterrupted power delivery when plugging or unplugging devices. It works well with low-power devices like routers (using a USB-C to 12V cable), making it a viable option for backup power needs. The remaining capacity is displayed via a simple but effective light-up percentage indicator that's easy to read in sunlight but slightly too bright at night.

The long but slim form factor makes it easy to fit in bags, including backpacks and laptop bags. At 580 grams, it’s not the lightest option, but its weight is reasonable given its high capacity, and 18.8 cm length and 8.1 cm width allow it to slip into most storage pockets in bags. While providing robust protection if dropped, the shiny plastic finish is prone to scratches. These marks are cosmetic and do not affect performance, though a sleeve can help mitigate them – albeit with some added bulk.

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ZMI No.20: Price & specs

ZMI No.20: Test results

I conduct comprehensive testing of every power bank I review to ensure they meet their manufacturer’s claims. The ZMI No.20 delivers outstanding results and runs slightly cooler than competing power banks, with no observed throttling in normal use.

During testing, the No.20 output 87.9% of its capacity at 20V and 84.9% at 9V, which is above-average efficiency. It sustains 100W output on a single USB-C port or 100W + 45W across both USB-C ports without overheating. The independent USB-C ports ensure that plugging in a second device doesn't cause the first to disconnect or renegotiate power levels.

The 210W total power rating is achieved using the first USB-C port (100W) and the USB-A port (100W) with the included ZMI USB-A to USB-C cable. Connecting two 100W laptops is possible, though if both use the full 100W for an extended period, the power bank may reduce the output. After efficiency losses, the power bank can easily fully charge most laptops, giving double (or more) runtime.

When recharging with a 100W charger, the No.20 hits full capacity in about 1.5 hours (and 80% charge in under an hour), or 2.5 hours when using the 45W input.

The ZMI No.20 uses high-quality Samsung INR21700-50E cells, which typically provide better cycle life and long-term reliability compared to the pouch cells in lower-priced power banks. This makes it ideal for frequent, heavy use.

Should I buy the ZMI No.20?

Buy it if...

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Also consider

The ZMI No.20 is one of the best premium power banks available, but below are a few other options if you are looking for something different.

How I test power banks

I get hands-on with every power bank I can and perform extensive testing in both the lab and real-world scenarios. Using equipment like the ChargerLab POWER-Z KM003C, I check charge voltage, protocol support, and log capacity tests.

Each power bank is also tested with real devices, including phones, tablets, laptops, and more, and then connected to a programmable load tester for multiple charge cycles. I carry a selection daily in both pockets and bags to assess their durability and ability to withstand rough, everyday use.

All measurements and weights are personally verified, ensuring accuracy beyond the manufacturer’s listings.

Want to know more? Read about how we test.