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While there is no lack of options for power banks on the market, very few offer the option of replaceable batteries.  Why would you want replaceable instead of sealed?
  1. Sealed power banks mean when the batteries lose capacity in 4-5 years, the item becomes disposable.
  2. If you have additional electronics such as headlamps or flashlights that can use 18650 batteries, a modular system is much more flexible and efficient than sealed power banks. I love pairing these with an 18650 headlamp such as the Skilhunt H03 or Wowtac A2S.
With these devices, you can simply swap batteries between devices for instant power, rather than charging over USB which is slow and inefficient.  From research I’ve seen on the web, you typically will lose around 30% of the capacity by charging over cable, so a 10,000mAh power bank is more like 7,000mAh.

What should you look for in a power bank with replaceable batteries?

  • Number of charging bays: For me, 2 slots is the sweet spot. The best batteries right now do 3500mAh each, which only can get around 1-2 charges on a modern smartphone.
  • Input charging rate:  High capacity 18650 batteries can take a long time to charge, so you really want a minimum of 1A.  Many inexpensive chargers only do 0.5A which can take 7 hours or more to charge
  • Output: A minimum of 2A should be available to charge larger devices like tablets, and also can improve charge times on smartphones. 1A is simply too low power these days.
  • Closed vs. open design: Some products try to save weight by leaving the battery compartment open (like the Nitecore F1/F2), but in my opinion this is a bad choice for travel where you want to throw the power bank in a backpack
  • Overall weight: I like to keep my travel weight as light as possible. The compromise here will be number of bays, the display, and open vs closed style

Let’s take a look at our roundup of 1 and 2-bay power banks:

1. Xtar PB2 
Pros: The Xtar PB2 is one of the newest chargers on the market, and our favorite. With a clever magnetic design, it is simple to swap batteries in and out of the device without worry about a sliding door breaking.  Additionally, it can charge at a rate of 1A x 2 batteries, which means a pair of 18650’s can charge in around 3 hours, much faster than slower charges that take twice as long.
Cons: The screen provides a convenient battery charge level. However, the blue light is rather bright when charging in a dark room.  Additionally, since this is a new device we wish they would have used USB-C PD for the charging input port.  Micro-usb is old and the ports tend to fail often.
2. Tomo M2

  • input: limited to 1A for 2 batteries, which means slow charging
  • output: 2A max
  • weight: 54g (1.9oz)
  • screen: backlit LCD, green
  • Buy the Tomo M2 on Amazon
The Tomo M2 is the first power bank I tried while traveling. While I had a lot of hope, this device fell short.
Pros: There isn’t much competition, and it does what it promises.  Charges 2 x 18650 batteries and works well as a power bank.
Cons: Charging is limited to 0.5A x 2 batteries, which is very slow.  The microUSB input port was very loose from the start, and now barely holds a cable in after only a few uses.  The screen stays lit while charging the entire time, which is large and backlit.
3. Nitecore F2
The Nitecore F2 is a variant of the F1 model for 2 batteries.  While I had a lot of hope for this device because of the ultra lightweight specs, it didn’t work for me in the end.
Pros:  Incredibly lightweight
Cons:  While charging batteries, a high pitched pulsing whine existed for hours on end.  This was with high quality NCR18650GA batteries.  I also found that I just dislike the open-style battery compartments.  While that keeps weight down, it means I can’t easily toss it in a backpack and not worry about it.