The "Your Fitbit Ionic is running low on battery" notification arrived on my phone and in my inbox at the same time around one yesterday afternoon, suggesting I take a moment to charge my smartwatch. Instead, I went to a couple of meetings, took the train home, went for a brisk walk with the dog, and made dinner. When I glanced at the watch again eight hours later, I'd lost only three per cent of my battery. Fitbit has solved the most critical problem of smartwatches by making a device with battery life so good you can excuse a whole melange of flaws. If every smartwatch lasted as long on a charge, we'd be in a whole new era of wearable computing.