Going wireless, whether you’re talking about a mouse, a speaker or a pair of headphones, is wonderfully convenient: who wants to worry about cables getting tangled up or snagged? But there are downsides too, and the most obvious of these concerns the battery. Apple’s AirPods wireless earbuds have what you might call a primary battery life of around six hours, before you have to put them back in their case for charging. That’s time when you can’t listen to music, but at least you can do it on the go. But after around 30 hours the case itself will be drained of power, and at that point you’ve go…