Only 3 years? We've had our car for 7 years and have never had a problem, other than the battery going dead a couple of times when my wife left the lights on.
The battery in my 5-speed has a date stamp of 2003 on it. I've run it down a couple times and recharged it and had no problems with it. Drove it all last winter with no problems.
If you (or someone else) bought a "top of the line" aftermarket battery, it usually is accompanied by thicker plates, and more durable internal spacers and associated hardware......these can be expected to last somewhat longer. I believe that the most robust battery that is available today has a warranty and design life of 60 months (5 years). Bear in mind that batteries like tires are warranted on a "prorata" basis, which means that if you have a 60 month battery, that fails in its 59th month, its going to cost you $95 bucks to replace it (under warranty), when you could have bought the replacement outright for $100.
The typical failure mode for a battery is that the lead plates are gradually eroded by the internal electrochemical reaction that makes them work......after they become so thin, they start to warp, due to the heat generated internally by the charging cycle, and eventually a plate will contact the next plate, creating an internal short (shorted cell), and failure. Also the buss bars that connect the cells in series are made of the same material, and erode as well, until they separate, resulting in a instantaneous catastrophic failure manifested by "zero" output volts.
However for the OEM batteries, and the "middle of the road" replacements, they typically come with a 36 month prorated warranty because their internal construction places their design life at that point (36 mo) in the most harsh duty conditions in the US. If you live in the south, or other areas where the battery is not exposed to extremes of cold, and frequent maximum cranking current drain, they can be expected to last a while longer. Even cars in northern climes that are garaged will see longer battery life.
That said......if your battery is seven years old, and you depend on it to start every morning to make a living, I would consider replacing it prophylactically, as it's definitely living on "borrowed time". Batteries are relatively cheap, compared to the frustration of dealing with a dead one. Also, "Murphy's Law" will likely apply, and the damn thing will roll a seven on the day you need it most.
doc
