Battery Life Span?

Batteries that have been maintained decently generally don't fail suddenly when camping. The usual failure mode is to gradually lose capacity until one deems the capacity insufficient for one's needs. There are of course exceptions, but I don't know that such exceptions are really correlated with age--in other words, it's not obvious to me that older batteries are more likely to catastrophically fail than younger ones if both seem to be in OK shape to begin with.

If the batteries you have seem to be serving you well, there's no reason in my estimation to replace them just for the sake of replacing them.