Have you noticed that your light may have not been running the length of the expected time on your last ride? Other than this being attributed to a mechanical failure of the light and possible warranty situation, there can be other factors that affect run-time.
1) The older the light, the less the run-time will be. Our Li-Ion batteries have an estimated 300-500 charge cycle capacity. A product that is used in optimal temperatures, is charged after every ride, and has avoided being stored for long periods of time can achieve a 3+ year existence, operating to their specified run-times. It shouldn't be until after years of use that a light shows more than a 10% decrease in run-time. Expectedly, a 5 year old light will have significantly less run-time.
This also applies to the external batteries used for lights such as the ARC, Stella, Seca, and Imjin.
2) Lights that are used in freezing temperatures can temporarily display low run-times. Much like the slowing of molecules in water when you place them in the freezer, the metals in a battery also become slower, so energy transfer becomes less efficient. Thus a poorer performing battery the colder it is. Our lights are rated to run optimally between 40-90 degrees Fahrenheit.
Lights in desert conditions where temperatures are well over 90 degrees Fahrenheit will tend to overheat, much less be affected by run-time, and the light will instead reduce output to try and stay cooler. This thermal rollback prevents the internals of the light from being destroyed.
3) Is the light charging fully? Most people will plug in the light and leave it over night. But, did you remember if the indicator light showed a solid green when you went to use it? If using a computer to charge your lights, you may walk away and it falls into sleep mode or maybe you close it. Its at this point most computers shut down their USB port and the light will fail to charge. Using an unreliable wall adapter can also prolong the charge time, or even not charge at all. Always check your charge sources to make sure your lights will be ready to go on your next ride!
To see if your light is preforming correctly, try a run-time test and meets the listed specifications.