Russell, I replaced my oddysey cub type battery a couple of years ago in our 391B, the previous owner had good luck with it, but didn't fly it in winter much. Oddysey makes one which is half again as thick, but still fits nicely in the original battery box with some shims. It has been great for us, and has kept cranking when I have made mistakes in starting procedures, and much appreciated in the winter. I will get the model number for you, but it was available off the shelf at battery specialists in Anchorage.