I had the same problem with my vv device. If I was using ultrafires or trustfires.. sometimes the mod wouldn't fire, I would have to take a batt out, put it back in and then it would fire one more time and then cut off. There is some reason that your batt's protection circuit is cutting off. It is probably your carto. Mine works fine on new(ish) attys and cartos but if they get some juice gunked up it will cause them to read a much lower resistance and cause your batts to trip. You can solve that by using aw imr's or just using another atty/carto or maybe doing a burn to burn the gunk off.