As luck would have it I'm in the market for 4 of them myself, I got 10 years out of the factory units and 9 out of the DEKA ETX 30L batteries (shorter lifespan due to the constant fluctuation on the Aux batteries I'm guessing). The DEKA's are USA made and about $144 on ebay, but I was told by a DEKA dealer prices are going up.
Just search for "ETX 30L" and it should bring up information on it, they are the same batteries that are used in Harley's.
Just search for "ETX 30L" and it should bring up information on it, they are the same batteries that are used in Harley's.