I found this site that has some great reading on Battery life,use and care
I've always believed that the Modern battery is built far too cheaply and too readily replaced.
it makes sence to me that a major boat battery Mfg would preach proper use/care for long term reliable service. 
" there aren't service stations on the water"

http://www.boatelectric.com/surrette.htm

Technical Bulletins
#501 - http://www.boatelectric.com/surrette.htm#501  - A SULFATED BATTERY
#503 - http://www.boatelectric.com/surrette.htm##503 -Maintenance Free or Gelled Electrolyte Batteries
#504 - http://www.boatelectric.com/surrette.htm##504 - Marine Battery Design
#505 - http://www.boatelectric.com/surrette.htm##505 - Marine Battery Ratings
#506 - http://www.boatelectric.com/surrette.htm##506 - Winter Storage
#507 - http://www.boatelectric.com/surrette.htm##507 - Battery Charging and Systems
#508 - http://www.boatelectric.com/surrette.htm##508 - Low Maintenance and Maintenance Free Batteries
#509 - http://www.boatelectric.com/surrette.htm##509 - Preventative Maintenance of Rolls Deep Cycle Batteries
#600 - http://www.boatelectric.com/surrette.htm##600 - Activating Instructions for Diesel & Marine Batteries

Dan Stevens
Volskwagen CLub of Central New York
http://autos.groups.yahoo.com/group/VWCCNY/