Googled this real quick:
http://www.tirereview.com/article/86...batteries.aspx
Bottom line, batteries are "entombed" in the assembly, you can't replace them. However, life expectancy is 5-12 years.
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2011 Le Mans Blue M3// Black extended Novillo w/ Blue Grey Aluminum trim/DCT/ZTP/ZCW/ZPP/ZCP Premium Sound ///Akrapovic Evolution Exhaust
2015 Audi S4 Prestige, Brilliant Black S-tronic
2012 Le Mans Blue 135i M Pkg DCT