Charging up a smartwatch every night is a pain in the ass. But what if you only needed to charge it once every 21 days? Enter the 46mm Xiaomi Watch S5. Xiaomi first released the Watch S5 in China back in March, but the company launched it internationally this week, with global availability starting in late May and early June depending on the region. While the Watch S5 hasn’t been announced for the U.S., the European pricing (€179.99 or €199.99 depending on the color and strap style) gives us an idea of what to expect should you want to import one. You’re looking at somewhere around $210 to $233. How exactly does Xiaomi’s Watch S5 get up to 21 hours of battery life when competitors like the Apple Watch Series 11 ($400) and Samsung’s Galaxy Watch 8 ($350) can only muster around a day? There’s always a big asterisk next to battery life, but in this case, it seems pretty reasonable. Light use of the Watch S5 allows the 815mAh battery to last up to 21 days.…