Just complied with SI0018 Carbon Cub Backup Battery. This is a well done kit by CubCrafters. Looks like it is standard equipment starting with SN154.
One caution. The positive and negative terminals on this battery are very close together. With the battery in bracket assembly those terminals are also very close to the bracket frame. I included a little insulation around those terminals just in case. CubCrafters did include extra insulation on the positive lead near the bracket.
By the way where are the SI's on the CubCrafters web site? I see SB's and SA's on the Support web page but no SI's.