New car battery - $150 (Dayton)

New Diehard car battrry, 600 CCA, size 124R.
Bought it brand a few weeks ago (have receipt).
Ended up selling the car it was installed in to someone who didn't need a battery so I took it out.
Car was only driven about 20mi (if that) with the new battery in it.
Been on a battery tender every since so it's in perfect condition.
Already have a new battery in my other car so I can't use this one.
Battery is $200 at auto parts store.