I was afraid they were going to pull that "unfavorable user behavior" BS on you.
It's shameful for BMW to sell an expensive car that a "normal" non high mileage driver can't depend on.
The new BMWs with "regenerative braking" are even worse as they now disconnect the alternator from charging the battery during acceleration and other driving conditions.
If your battery does fail under the warranty / maintenance period I'd push the dealer hard for replacement (did that successfully).
All that said, a battery tender is an inexpensive peace of mind accessory to top off your charge!
"sometimes you're the windshield .... sometimes you're the bug"
2014 328i Mojave Metallic
2009 328i Black Sapphire Metallic
2007 328i Black Sapphire Metallic
2007 Honda S2000 Berlina Black
(Hey Jim... am I diversified?)