Bennett batteries for stored energy systems (SE)
Other types of sealed lead acid batteries were not designed for use in these systems as the charger board was designed around these batteries. They have a different internal resistance, amongst other specs.
Portable Power Systems normally has about the best price on these batteries. These batteries are actually two 6 volt cells glued together and jumpered to make a 12 volt battery. I've found that the solid wire jumper with push on connectors have the fewest problems as the spot welded piece of metal jumper material, may, at times, not carry the current and create an "open" between the two 6 volt batteries connection. The downside to the push on terminations, they sometimes will corrode over several years.
Click on the battery  above for the website link to Portable Power Systems. Their price currently is about $32 per battery for 30 qty.
HOLDEN BATTERY SERVICES, LLC

TOLL FREE: 800-594-9257

PHONE:276-466-4713

FAX: 276-466-4080 EMAIL: PTHOLDEN@AOL.COM

http://www.x-raybatteries.com/

Enersys (Hawker) Cyclon 0819-0020 D-Cell 12 Volt/2.5 Amp Hour Sealed Lead Acid Battery
And another source for these batteries
is listed below: