FLEXTAIL Zero Power Bank Review

Over the last five months, I’ve been testing the FLEXTAIL Zero Power Bank. FLEXTAIL sent a sample for review. When looking for a modern power bank for canoeing, kayaking, and all the other outdoor sports I do, I have a few criteria. I want a bank that squeezes the most power out of the battery, has fast charging when needed, has cold resistance, USB-C, pass through charging, water resistance and weighs very little.

Some of those criteria conflict with each other. Fast charging, for example, reduces usable battery capacity. Newer power banks like the FLEXTAIL Zero Power Bank offer lower-power efficiency modes that trade charging speed for longer runtime and broader device compatibility. This gives the user options.

Get it: Direct from FLEXTAIL, Amazon

What is the FLEXTAIL Zero Power Bank?

The Zero Power Bank is marketed as the world’s lightest and thinnest 10,000mAh power bank.

The bank itself weighs 143 grams (5.04 ounces) on my scale. The included USB-C cord weighs 7 grams (0.25 ounces). It also ships with a lanyard, which weighs 5 grams (0.18 ounces). Together they weigh 155 grams (5.47 ounces) on my scale.

The lanyard cable is a USB-C cord that doubles as a lanyard. The connecting piece docks the ends of the cord and protects it.

Battery Capacity

The battery capacity is 10,000mAh, but the usable capacity varies by the mode: 7,000mAh in Efficiency Mode (5V-1A) and 5,200mAh in Fast Charge Mode (12V-1.67A). Input is 18W max (5V/9V/12V), and output is 22.5W max.

Some of the competition claims that they can get more juice out of a battery in a fast charge mode. One direct competitor claims 6,800mAh while fast charging.

Two Charging Modes

A single press of the button activates the Fast Charge (22.5W, green LED), which FLEXTAIL claims can bring an iPhone 15Pro (3274mAh battery) to 50% in 26 minutes. On my Pixel 6 (4614mAh battery), it took 27 minutes to go from 10% to 50%, and 105 minutes to 100%. A double-press activates Smart Efficiency Mode (orange LED), which runs at a lower wattage but delivers 30% more usable power. Another double-press switches the bank back to Fast Charge.

Battery Indicator

The battery indicator has four LED lights: first light = 0–10%, second = 10–50%, third = 50–75%, fourth = 75–100%. During testing, these didn’t seem to be exact. For example, after charging my Pixel 6 it still showed three bars. I drained my Pixel 6 again and tried charging it a second time, the bank died before fully charging the Pixel 6 a second time.

Materials & Durability

The cover is forged carbon fiber that is compression molded from shorter fibers. FLEXTAIL claims the forged carbon fiber shell improves strength while keeping weight low, though like any lightweight power bank, it still deserves careful handling.

It has a IPX4 water resistance rating. That means that it can withstand splashes, a little light rain, but it isn’t waterproof.

Emergency Reserve Feature

An auto-stop feature locks the last 10% of battery as reserve. FLEXTAIL claims that charges a phone to about 30% capacity or enough for an emergency call, GPS fix, or to charge a headlamp.

FLEXTAIL Zero Power Bank in Use

I’ve used the FLEXTAIL Zero Power Bank over the last five months to charge my various pieces of gear. One instance that stands out is when it saved my tablet during a visit to have maintenance done on my car. My tablet had completely drained, and I forgot the charger at home. I was able to charge the tablet while watching videos for a course that I’m taking.

Other than that it has charged all my devices. I had some concerns about older devices that use the USB mini connector, like my Garmin bike radar taillight. I have a converter that plugs into the end of a USB-C cable and converts it to a Micro-USB. When using the Micro-USB connection in this way, the devices won’t communicate to each other. The power bank should fall back to the lowest charge rate, but I didn’t want to risk it. So, I only used the Efficiency Mode when charging the radar. This is something to consider if you have older devices.

Passthrough Charging

I did try passthrough charging, and it appears to work. My phone charged at the “slowly charging” rate instead of fast charging while the bank was connected to power. While it works, it’d likely be faster charging both devices separately. When paddling this isn’t likely to be an issue unless you’re resupplying in town and trying to charge devices quickly. I think it’s better to pack a charger with two ports instead.

With a Solar Panel

Lastly, I tried charging it with my old Kickr IV solar panel. The Kickr IV is a 6W, 5V regulated panel, so at peak output it runs at about 1.2A. While older by modern standards, the panel still represents the kind of small solar charger many paddlers already own. It charged the battery. I didn’t do a full charge, but in direct sunlight with the panel flat on the ground, it slowly charged the FLEXTAIL Zero Power Bank. In normal conditions that one might face in the Boundary Waters Canoe Area Wilderness, it might take all day to charge that bank using my panel. I don’t use solar anymore for my trips. I just carry extra batteries. If you do, the FLEXTAIL Zero Power Bank accepted trickle charging from an old panel, so it would likely do much better with a modern 10-15W USB-C panel.

FLEXTAIL Zero Power Bank Conclusion

During my testing, the FLEXTAIL Zero Power Bank seemed to perform well. It’s a nice power bank and one of the lightest on the market. The Smart Efficiency Mode gets a lot of power out of the battery, which appeals to me. Compared to typical 10,000mAh power banks that weigh 6–8 ounces, the FLEXTAIL Zero is unusually light.

Pros

• Extremely lightweight for a 10,000mAh bank
• Efficiency mode improves usable capacity
• USB-C and passthrough charging
• Accepts low-current solar charging
• Compact form factor

Cons

• Fast charging significantly reduces usable capacity
• LED battery indicator lacks precision
• IPX4 is splash resistant, not waterproof
• Premium pricing compared to conventional banks

Get it: Direct from FLEXTAIL, Amazon