The problem with anecdotal accounts on-line like;
"I bought Interstate batteries and they died in two years, Interstate batteries suck."
"I bought Trojan batteries and they are still going at year 7, I love my Trojan's."
is that these are simply anecdotal. Without using industry standardized test equipment, which almost no boater owns, and industry thresholds for "failure" as 80% of new capacity, these anecdotes are pretty much useless as we have no control or baseline to work from.
Exactly right! This is a relatively simple concept which most folks just don't get. I don't know why.
Put in the simplest terms I know of:
1. all batteries begin to deteriorate from the time they leave the factory;
2. this deterioration is the result of numerous factors, though chiefly sulfation -- collection of PbSO4 lead-oxide crystals on the plates, leading to reduced surface area; and
3. this means that over time batteries LOSE CAPACITY (not charge), i.e., the ability to deliver energy anywhere near their rated amount.
Your batteries might still show a healthy charge, but have only a fraction of their original capacity. You can't measure capacity with a voltmenter....you need either a sophisticated (and expensive) measurement instrument or you would need to do a controlled and measured 20-hour load test.
Anecdotal statements of the type MaineSail mentioned are practically meaningless. "I got 5 years out of my house batteries" or "My house batteries died after only 2 years" are meaningless statements....unless they are accompanied by hard data on remaining capacity, use and treatment of the batteries over their lifetime, etc., etc.
Think of it this way.... Your car battery is no exception. So long as it starts your car, you think it's "good". That cold morning when it fails to start the car, it's no longer "good", and will likely be replaced.
The truth is that it takes relatively little energy to start a car....typically less than 1/2 amp-hour. Your battery has been losing capacity since the day it left the factory. You just didn't notice because it still could deliver the 0.5AH of energy -- in a burst -- to start your car engine.
Truth be told, you had no idea whatsoever that your battery was on its last legs, i.e., had lost most of its original capacity.