I bought a Mercedes brand battery for my car (a '98 e300) from a Mercedes dealer about a year ago for $160 (there was a 10% discount). I installed it myself. The previous Mercedes battery had lasted 8 years and nine months.

The cost was less than the priced quoted over the telephone by Sears ($225) and by two chain auto parts places, Auto Zone and another one, can't remember the name (about $190).