I find the most common problem with cheaper lights is the little metal connections that the batteries touch or connects whatever else to whatever get squished down and don't connect properly, pull it apart and pull them all up a little with a small flathead screwdriver.
I find the most common problem with cheaper lights is the little metal connections that the batteries touch or connects whatever else to whatever get squished down and don't connect properly, pull it apart and pull them all up a little with a small flathead screwdriver.