Made a cheap but effective bottle warmer for my 1lb bottle last year. Go to Target or Walmart and buyy a babies milk bottle warmer. Get the kind that has the adjustable warmer strap. All ya got to do is cut off all the housing support plastic not needed and tie in the hot and ground lead to your battery. What good about this bottle setup is that it is small, very low drain and that it comes with a built in switch (push botton to turn on) and has a red LED that lets you know its on. I put a separate toggle switch between the battery and bottle switch just to be on the safe side. Works great and heats the bottle quickly...If I'm not mistaken there is a auto shutoff too. Cost : about $10.00