OP, I still don't understand how dealer can say the battery is not under warranty. It should last the 4 years, 80k original warranty you have.
Past: '89 Olds, Alpine white e46 323i, Jet Black e39 530, Saph Black e60 530, Space Grey N54 e92 335, Mineral White N55 e92 335
Current: '13 FO e92 M3, Swifts, Akra Evo ... otherwise trying to stay OEM as possible!!