Mine was never as bright as my mate's from day one. (His MED was my high!)
Anywhoo, I removed the annoying 3 mode driver (found swarf, bare cables and hardly any heatsink compound inside) and fiited an external DX 2800ma one/ switch. Looks horrible, but now proper brightness and a simple on/ off 🙂
also had prob with the battery. it gets wet and the IC on the balance circuit gets wet; this means it shows charged when it isnt.
Super brightness though and still hasnt really cost anything. Just bought a 1×18650 powered p7 torch to decorate my helmet