If your regulated device only goes up to 12.5watts, I'm going to guess that it probably has an amp limit of 3.5, so the lowest resistance you can use is 1.2 ohm to get the max output on it. I don't specs of protected batteries since I don't use them, but all reputable 18350 IMR's that I've come accross have a 6amp or higher rating, so stick with Efest, or AW for best life, safety and performance. If your batteries are protected and have an amp rating higher than 3.5, then you should be good to go at your own discretion.