I've been using my drill batteries for years for power my 12V power system. I had each of the 4 batteries connected with a 'rube goldberg' bracket, but decided to design and 3D print a modular bank to connect all 4 of my batteries in parallel. On the side of each bank, I have holes to tap a bolt against each of the + and - terminals of the batter. At the end, I can have 1 main terminal.
I'm currently printing a 2nd adapter for the middle batteries.