My battery is about 4 years old so I decided to replace it. This time, I went with a LiFePO4 battery. It only weighs ~4.5 pounds and should last ten years. I think this is a no-brainer upgrade for anybody who wants a lighter car or just wants a battery that will last forever.
Here's a link to the exact battery I bought. It is a little more pricey than a regular battery but, again, it will last twice as long. $215. If you get on that company's mailing list, they often send 10%- or 15%-off coupons.
The red goo on the terminals is anti-corrosion stuff.