As I need one for my Highline. The japanese made ones and Bosch are pretty expensive, at least double that price, not to mention BMW's price.
Someone offers here Hyundai batteries from Korea at 73 $.
Details
Capacity
at 20HR
Rate
(AH) 85

Cranking
Performance
at 0˚F
(Amps) 450

MAX. Overall Dimension(mm) ght
Length Width Height
357L Ｘ175W Ｘ175H (that fits perfect, 175 is max for electric rear seats)

weight w/o acid
16.2 kg

Acid
Volume
(Approx. ℓ) 5.4


http://page11.auctions.yahoo.co.jp/jp/auction/n47114738



One question regarding:

Cranking
Performance
at 0˚F
(Amps) 450

How is that to comparable ones in the US you are using?