Cable, bracket and screws: [URL] Bear in mind that you'll be reducing the battery runtime  by a factor of 2 -- and with some configurations (particularly those with a QHD screen), the system may not run at all with the smaller battery -- and certainly won't run for long between charges.  
I have a  Dell XPS 15 7590 and I have two questions adding a second SSD hard-drive. 1. Is this even possible and/or supported by Dell? I assume this can be done as the official service manuals reference a second 2.5" hard-drive. I also see from this previous post ([URL] that I will need to purchase the smaller, half-width battery in order to make room for the second drive   2. Assuming that I can add a second SSD hard-drive, where can I find what additional parts I will need to purchase? I know I will need a smaller, half width battery (and a new 2.5" SSD), but is there anything else? Judging by the service manual, it looks like I'll also need a hard-drive cage and a hard-drive cable (and possibly some additional M2x4 mounting screws). The "official" parts and accessories page for the XPS 15 7590 ([URL] does not appear to list any of those items apart from the half-length battery.
Dell XPS 15 7590 - Is is possible to add a second SSD hard-drive?