Best answer: The Samsung Wireless Charger Duo can charge more than just the new Galaxy Watch. It can also be used with the Gear S3 Frontier, Gear S3 Classic and Gear Sport. It isn't guaranteed to work with any earlier Gear smartwatches.
Amazon: Samsung Wireless Charger Duo ($115)
You can also charge the Gear S3 series and Gear Sport
Samsung's new Wireless Charger Duo was designed with the latest Samsung phones and watches in mind, but it actually has backwards compatibility with the last generation of Samsung smartwatches as well. In addition to the new Galaxy Watch, you can also charge the last-generation Gear Sport, Gear S3 Frontier and Gear S3 Classic.
All three of these older watches use the same charging system as the new Galaxy Watch, called Qi wireless charging, and can be used on one another's chargers interchangeably. That cross compatibility extends to non-standard accessories, like the Wireless Charger Duo.
The Gear S2 series — both the standard and Classic — smartwatches also utilized Qi charging, but Samsung doesn't guarantee compatibility with those older watches on this new charger. The standard Gear S2, in particular, won't fit on the charger properly because of its inflexible bands. You may have a shot at getting the Gear S2 Classic to work with certain bands, but we can't say it will work for certain.
A nice dual charger for the last two generations of Gear smartwatches.
The Wireless Charger Duo works with the new Galaxy Watch, but also the still-great Gear Sport, Gear S3 Frontier and Gear S3 Classic smartwatches. You should not expect to use it with any earlier Gear smartwatches.
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Andrew was an Executive Editor, U.S. at Android Central between 2012 and 2020.