Actually Oldfarmer, 3-4 years of life for conventional lead-acid deep cycle batteries is fairly short. If you look at the lifespan table in section 7 of this link, you'll see that marine and golf cart batteries can last up to 6 years, and I have seen some that lasted up to 8 years.
http://marine-electronics.net/techarticle/battery_faq/b_faq.htmI've also seen lead-acid stationary and traction batteries that lasted 20 years or more. It all depends upon how well they are maintained and monitored. Standard chargers do a good job on batteries in good condition, but sometimes we neglect and abuse our batteries by incorrect charging, discharging, and by the environment or way they are used. That's where some of the types of chargers Replacement mentioned earlier really shine. The new technology smart chargers can reverse damaging sulfation that causes premature failure, and they utilize microprocessors to deliver the charge in an optimal manner.
I kinda cringed when Sam mentioned finding a bunch of discharged batteries in a storage shed. Depending on how deeply discharged they were, and if the shed is unheated in his Nebraska climate, they may have suffered damage that a conventional charger cannot overcome. They may still take a charge and seem OK, but their capacity and overall life may be reduced. Batteries aren't getting any cheaper. Proper maintenance and a good smart charger can quickly pay for itself. But as Replacement also pointed out, there are differences in batteries and smart chargers. Very good information is available for folks who want to get the most out of their batteries.
