Its probably a hold down point, but check continuity between it and the stud on the right. If there is continuity then battery power can be attached there also
It's primary intended for interlocking/linking additional units together(they're scale'able) ......For example, if you had two of those, you could pop off the seconds ones right side (ground buss side as shown below) and slide it into the firsts ones left side (note below [and on yours] the undercut/overcut end edges on each and their removable/snap off ground buss sections)
