I bought two honkin' big 12V's this summer. The old ones were toast, used since 2013. Bought the new ones at Canadian Tire in Prince Albert. Total was close to $380. Yes, I know two 6V's would be better, but I have two nice big 12's.
Our old Sub has two batteries in it, but our main TV only has one. I doubt I need to worry about dead batteries on a night or two with out SP.