I used to replace them every year or two,thinking i'll catch it before it fails.
I've since been waiting until they fail,but it's been 3-4 years,and they are still going strong.
I make sure they are mounted in an easy spot to get to,and carry spares,so I can swap them in a min or two if they ever fail.I do clean and grease the connections every year,so they will come off easy if I do need to change it.