As one of the many who cannot attain minimum weight, I went thru this excersize myself. Optima is heavy (and expensive). Rule that out right now. Here's the Walmart solution I found:

Go into Walmart, and throw a bath scale in the cart. Then push it over to the car battery area. Weigh youself holding all the batteries available that fit your car. If you don't know the right battery - Walmart even lists the correct ones for you car. I found that the absolute lightest one (that was correct for my car) was also the cheapest one (about $30). Isn't it great when that happens! When I replaced the "Diehard-Super-Gold-Whatever Battery" I had, I lost about 15lbs!