Des Yap did some initial testing of the new $649.99 T-Rex Dual Solar from Amazfit — the first endurance watch with a bright and colorful OLED to be fitted with teeny-weeny solar panels. The ring around the display can extend life a bit, but the larger rear panel around the heart-rate sensor can add a few percentage points of charge when you arrive at camp, or when the watch is slung off a running vest, so maybe you can leave your ultralight power bank home on your next multi-day adventure.