Could you run a couple 6 volt batteries in series giving 12 volts and same Ah of each individual battery?
I found Duracell 6-volt coil-spring terminal lantern batteries with 13 Ah online at batteryjunction.com for $6.95 each. (http://www.batteryjunction.com/duracell-v6.html) They also have the larger screw terminal Duracell 6-volt lantern batteries with 27 Ah for $14.95. (http://www.batteryjunction.com/duracell-mn918-6v.html) They’re sealed so scent shouldn’t be there. I know the smaller 6-volt lantern batteries are just filled with AA batteries.