Incredibly, Swedish audio brand Urbanista's noise-canceling Los Angeles headphones don't need to be plugged in for charging. Ever. The top of the headband is lined in photovoltaic material that constantly trickle-charges the battery--which has a massive 50-hour runtime--from any light source.
Which is to say, you don't need direct sunlight to charge them. "Los Angeles converts all light, outdoor and indoor, into energy to deliver virtually infinite playtime," the company writes. "Los Angeles never stops charging when exposed to light, providing you with a nonstop audio experience."
I can't tell you how handy these would come in here on the farm. Before running the wood splitter, wood chipper, the mower or the chainsaw, you must remember to have charged the noise-canceling headphones. Alas, there is no ruggedized nor outdoor version of these; the Urbanista brand, as the name implies, was formed "out of love for cities and urban life," according to them. What I need is a Ruralista sister company.
I checked out a few reviews of the Los Angeles and they're mostly good; these seem legit. As for how well the charging system works, "Don't doubt the efficacy of the charging system here," reads the TechRadarreview. "Or how smug it'll make you feel."