My battery is inside a cylindrical 2x4 inch container made by Viewtainer. It has rubber cap on both end to keep moisture out and sold by Home Depot. It rest horizontally behind my seat post and between the rack. I got the Y cable there going to my tailight and extension. A very small portion of the extra cable goes inside the container. The container is nice because if the battery ever does overheat and catch fire it is not inside my pannier bag where it can be hard to get at while I am on the train.

The extension run under the top tube most hidden by my oversized Airzound bottle. The MS front light is on an extender next to a flashlight. The wire is hooked to the extender cable and all extra cable is coiled up around the unused section of the bar extender and tape up to keep it uncoiling. I don't use a wireless bike computer so the coil wire or the cabling route will not be a interference issue.