Proper battery maintenance is critical, especially during winter months. Check for corrosion build up on terminal posts and cable ends, and use a battery cleaning brush to remove any that has built up. Cleaning grease and corrosion from the surface of the battery is important as well. A battery sealant can help prevent future corrosion. Testing the cold cranking amps, or CCA, can give you idea of how much life the battery has left. A good battery has 85% or more of its rated CCA, any less than that and the battery should be replaced.