This is just a matter of usage. MacBook Pro batteries have never lasted me more than ~3 years before signficant degredation (usually marked by swelling, needing

This is just a matter of usage. MacBook Pro batteries have never lasted me more than ~3 years before signficant degredation (usually marked by swelling, needing replacement to avoid having the touchpad eject from the machine), and that number held from pre-unibody to post-retina. As an anecdote, the later generations seemed to degrade faster than the earlier ones. Serviceable batteries are very important.