To check the batteries you should use a battery load tester. I have found that most batteries are good for about 3 years,4 if your lucky. Once you have to start jumping off the truck, it's time for some new ones. Also, buy the best quality you can afford. It seems to pay off. If I was to need new batteries now, I would go with the OPTIMA group 31 yellow top they seem to be awsome. When my red tops go, which might be in another year or so, I'll order them from Summit.