boat store or golf cart batteries.

http://www.batteriesplus.com/store_locator/state/UT.aspx

OP...... are you looking for 12V or 6V??  RV???

RV 6V.....for best money spent per dollar, Costco or Sams Club.  State Trailer has Interestate at about the best price

If you know anyone who manages a commercial UPS system find out what their battery replacement schedule is.  Most systems will have their batteries replaced completely every three to five years or have a phased replacement on a per string basis more frequently.  Either way the process requires large numbers of premium batteries to be replaced.  Often  a large number of them are serviceable and usable for a homeowner.  The disposal costs can be large so many of these installations are willing to give you the batteries or sell them to you for next to nothing.

As an example the facility work at has a 50kva UPS system.  I manage/monitor it as part of my duties however all maintenance is performed by specialist electricians. The system consists of two strings of batteries.  Each battery is about $450 new.  Over the 3 year life of the string many batteries will be replaced as part of normal maintenance so between these newer batteries and the dozen or so of the best other batteries you can usually find 15 or so that are extremely usable for homeowner backup power.

Find these systems and find out  what their replacement schedule is and if they will give or sell you the old batteries. You can get some awesome batteries for next to nothing.

Correct. Most of these batteries are low voltage around 3V I believe so you will have to daisy chain them together to get 12V.

I can't speak for all systems but mine uses 12VDC batteries made by Enersys. The HX series.  I have heard of systems that use 6 but 12 volts per battery is very common.

You are most likely correct.  The ones I had seen were in Power plants and refineries and were 3V they added up to get 125VDC for their back up systems.  But none the less, you make a great point about getting these types of batteries.

Paging Paul

The OP is vague, but I bought a 22Ah Chrome battery from:

ChromeBatteries

They get pretty good marks for the smaller types.

Shipping is included.

Chris

Check to see if you have an Interstate Batteries near you. They have new deep cell, but also some times have ones that been pulled from back up systems like they are talking about. I pick up some 6 moth old ones that were pulled from a hospital for $40 each