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Rolling Square TAU 2 Review

The Rolling Square TAU 2 is an effective update on the first iteration and is a capable emergency power supply, but it still feels large for a 2,000 mAh battery.

Our Verdict

7.1 /10
Good info






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  • The charging cables feel durable and add versatility
  • The materials have held up knocking against keys
  • 2,000 mAh capacity is great for topping up your phone battery


  • Footprint is large considering its 2,000 mAh capacity
  • The included charging cable isn’t the sleekest design
  • Removing the cover is challenging when you don’t have keys attached

Technical Details

  • Weight (oz)

    1.7 oz (48.2 g)

  • Dimensions

    2.375 in x 1.75 in x .45 in (6 x 4.4 x 1.1 cm)

  • Notable Materials

    Plastic, Metal

  • Manufacturing Country


  • Warranty Information

    Rolling Square Warranty

Full Review

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Before diving into the second iteration of the Rolling Square TAU, we wanted to explore why we didn’t love the first version to see how things have changed here.

Rolling Square TAU 2 Tau 1
Rolling Square TAU 2 | The first and second versions.

Our biggest gripe was that the battery was only rated at 1,400 mAh, which is incredibly small, especially for the battery bank’s size. It’s pretty big compared to other battery banks of the same size that came out around the same time.

Additionally, the metal hook was finicky, it could have been more user-friendly, and charging your device wasn’t quick and easy. Because of that, we didn’t reach for the first TAU as much as we would have liked to.

Luckily, these issues have been dealt with in the second iteration. That said, just because they’re changed doesn’t mean they’re perfect. Will they make us like this product more? Let’s dive in and find out.

The Rundown

If you aren’t already familiar with the TAU, it’s a keychain battery bank. Essentially, you’re meant to keep it with you all the time to charge your devices, and it attaches to your keys or anything with a clip or a jump ring. It’s roughly the size of a car key fob or a little larger, depending on what you’re used to.

Rolling Square TAU 2 Solo
Rolling Square TAU 2 | This thing is small!

The external materials are hard plastic, which feels durable enough to handle the bumps and knocks of travel. We haven’t had any durability issues so far, which is ideal. Nobody wants their battery bank to split in half while wandering through the Roman-era Chester City Walls.

On the end of the keychain, there’s an eye that you can attach things to. Additionally, this serves as a cover for the ends of the charging cables. It feels counter-intuitive to have the cover for the cables (which pops off to charge your devices) in the same place as the eye you attach to things; however, we have yet to have any issues with this popping off when we didn’t want it to. Still, we’re worried it may loosen and become a problem in the long term. Overall, we like this design better than the metal clip in the first iteration.

Rolling Square TAU 2 Cover
Rolling Square TAU 2 | Taking the cover off is easy.

The TAU has two charging cables. There’s a USB-C on one side and a Lightning cable that also works with micro-USB on the other. This creatively covers most of your bases while you are out and about. Figuring out the micro-USB takes a few tries, as it is integrated into the Lightning cable, but it’s easy once you’re used to it. The cables feel durable but are very short, which can be awkward in use.

The USB-C cable can charge the device or other devices, which is handy. Because you can charge the device on the go without the included charger, you don’t need to bring it on every trip. Additionally, it works for pass-through charging so that you can charge your device and the TAU at the same time.

On the bottom of the device, there’s a metal port. This is used to power up the device with the included charger. It is magnetic, so it pops into place and stays put. You can attach the charging unit to the wall or your desk to hang your keys for the night and to prepare for the next day with a fully charged battery bank. The cable hanging down the wall doesn’t look great, but it’s a unique idea. You can charge the device with the USB-C port and leave the cable at home when traveling.

Rolling Square TAU 2 Light
Rolling Square TAU 2 | The charging port and light.

A small light on the front of the bank has three colors to indicate how charged the device is. Red means 0—19%, orange 20—59%, and green 60—99%. Not making each color cover one-third is odd, but it is not an issue.

Last but not least is the battery itself. This iteration has 2,000 mAh power, a step up from the first iteration’s 1,400. Still, this is low, especially for the size. Using our non-math major measurements, the volume of this battery bank takes up roughly 1.87 square inches. We used this measurement, and those from other battery banks we often recommend, to do some non-mathematics major math on how efficiently these banks utilize space.

  • Rolling Square TAU 2: 1,069.5 mAh/square inch
  • Clutch Charger Pro: 1,533.7 mAh/square inch
  • NITECORE Carbo: 1,964.6 mAh/square inch

These are vastly different battery banks; however, the TAU doesn’t do well regarding footprint size per mAh.

Rolling Square TAU 2 In Use
Rolling Square TAU 2 | Using the device.

Taking our bad math out of the equation, the TAU is still useful. The battery bank will charge a standard iPhone 15 roughly 60% of the way, a solid emergency or battery-topper option. Still, it isn’t a lasting solution for most travelers who want more reassurance that they can get their boarding passes, use Google Maps, and check into their flights and hotels.

Additionally, you can use the TAU 2 as a digital ID to share your contact information with other travelers or business connections.


The TAU is pretty small despite all our talk about the mAh to volume ratios. It measures 2.375 in x 1.75 in x .45 in (6 x 4.4 x 1.1 cm), easily fitting into your pocket, in some travel pouches, and your sling or daypack. However, it feels quite bulky in some skinner pockets, as it’s close to two inches thick.

Rolling Square TAU 2 Key Side
Rolling Square TAU 2 | Compared to keys, it is big.

The device doesn’t add much weight to your keys, but it will add significant volume for people with only a few keys. That said, most people won’t notice a massive difference with the TAU next to their key fob and assorted keys.

When using the TAU, it easily fits into the palm of your hand and is easy to handle. The included charger isn’t the most portable, but you can leave that at home while you’re traveling in favor of the USB-C charging method.

Quick Comparison

One of our most recommended battery banks on the lower end of the spectrum size-wise is the Clutch Charger line of battery banks. The Clutch Charger V2 has a 3,000 mAh battery, the V3 3,300 mAh, and the Pro 5,000 mAh. Even the lowest from the Clutch still has a bigger capacity than the TAU 2; however, the latter excels in other areas.

Rolling Square TAU 2 Comparison
Rolling Square TAU 2 | The Clutch Charger is a good comparison.

With the Clutch Charger, you can only charge with one cable. That means you’re stuck with either USB-C or Lightning. With the TAU 2, you’ve got three to choose from, which is much better for traveling for people with multiple kinds of devices.

Additionally, the TAU 2 has a smaller footprint than the Clutch and is easy to attach to your keys, making it easier to bring with you (in theory). However, we’ve found that the Clutch is easier to carry in your pocket because of how flat it is, which makes it something we reach for over and over again.

Rolling Square TAU 2 Solo 2
Rolling Square TAU 2 | We dig the look of this thing.

Either of these battery banks is a solid option for a topper that will come in handy while exploring the world. Depending on the kinds of devices you bring and how you like to travel, one might make more sense than the other!

Usage Timeline

Initial Usage

Condition: Excellent

  • The materials feel durable and stuff—we’re curious if they’ll break-in
  • No issues with the topper coming off yet
  • We’re curious how accurate the 2,000 mAh rating is
2 Weeks of Use

Condition: Excellent

  • No issues with the materials or hardware
  • The battery charges quickly
  • We wish there were a little more power
By Eric Hergenreder
Created April 10, 2024 • Updated April 10, 2024
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