Bought a Movi Pro recently, it came with 2 batteries, that looked a bit scratched on the sticker, about 1-2 years old I guess. They seemed to last for a fair amount of time, maybe an hour while I was setting up stuff and testing out, not a lot of movement, but as they got down to 30-40% while stationary, sometimes if I maybe touched the gimbal/camera and the motors were working harder, it just died. Had to swap them around to get it back on again and it was fine for a while (with not much movement). So i'm considering buying replacement ones but would prefer to buy slightly used. Is there a simple test I can do to see the condition of the battery? Maybe put one battery in the Movi and see how long it lasts? Go by serial? Observe the way it charges? Something to do with the lights on the back on the battery corresponding to its power? I guess the same question again would be 'how do you know when it's dead'? It gives me different readings on the back based on how much it's moving.