My C20 from FastTech (https://budgetlightforum.com/t/-/16942) does the same thing. After I did the tailcap mod, it improved, but when the light is jarred against a hard surface, it goes to the blink-every-few-seconds mode. I didn't know that was the low battery warning either, thanks for the info! I know I'm going to have to take mine apart and replace the spring on the driver to improve contact as it's very annoying as it is. I may also take the opportunity to install one of the new 20ma-low Nanjg drivers from IO (https://budgetlightforum.com/t/-/17222) on this light...