The type of batteries for UPS service are primarily designed for float service and have a limited number of deep discharges. Having said that, several people have indicated that they have used them for several years very successfully. I would take them and use them if it were me.
This is a link to the Help board where several links are posted. Scroll down to the links regarding batteries:Click Here for Favorite LinksELECTRICAL SYSTEMS AND BATTERIES
CAR AND DEEP CYCLE BATTERY FAQ This consumer oriented FAQ contains answers and information about lead-acid batteries used to start car, motorcycle, truck, boat, recreational vehicle (RV), power sports, motor home, tractor and other engines.
BATTERIES--AND OTHER ELECTRIC STUFF 12VDC electricity first. 120VAC electricity follows. This starts with the basics then gradually gets more advanced, with more extensive tests and interpretations.
Bus Conversion Electrical Systems My Goal in writing this note is to help you design an optimized bus electrical system, and to help you avoid common mistakes in your systems that will limit performance, or create hazards.
Deep Cycle Batteries FAQ's This FAQ assumes a 12-volt, six cell, negative grounded, lead acid battery found in most recreational applications in North America. For six-volt batteries, divide the voltage by two; for eight-volt batteries, divide by 1.5; for 24-volt batteries, double the voltage.
Connecting Batteries & Chargers
These are just a few of the places you can read up on batteries & related items. There is lots more to batteries than just using them. If you treat 'em right, they can last a long, long time. Abuse them & you will be constantly replacing them.