The UB12500 Universal Power Group UPG batteries for approximately $100 bucks each sound pretty good. They are sealed AGM and claim 50 amp hours and weigh only 39.6 pounds. Also they are compact the specifications on this battery are Length 7.8 in., Width 6.54 in., Height 6.75 in.
I already have the Mars ME0709 72volt 300amp motor, and plan on getting the 7245 450amp Alltrax controller.
So for half the price of comparable Optimas can you tell me why I shouldn't buy them?
Have you looked into LiFePO's? They are arguably cheaper than lead considering their longer lifespan, and they be discharged deeper with less damage than lead. They need a BMS tho.