Interesting reading in the service manual about the battery. The parasitic losses with the energized systems they say the battery could go south if sitting more than a month (south meaning not enough to start the car). They recommend a charge or tender if longer. Makes sense to me so don't let it sit for long periods and charge/tender it if you do then battery should last a while longer. Anyway, lots of good info on variety of service life, if in doubt, swap it out!