Maybe the dealer's doing it that way for him at special request. The 'second battery' option on my TT was a dealer-installed thing and both batteries were the same so I think the dealer supplied them both. The only thing the factory did was have two battery trays.
And hasn't it been mentioned here that the provision of batteries is a dealer thing anyway? Especially with stock units, the factory has no idea how long they'll sit on the lot - why would they ship batteries that could die before the unit is sold?
2015 Rockwood Signature UltraLite 8282WS Platinum, GY Marathon LRD, TST 507RV TPMS
2005 GMC 2500HD CCSB D/A, Curt E16, Prodigy P2, Garmin RV760LMT w/BC-20 b/u cam