There are some USB power bank designs that use cordless tool batteries, but none that I found that work with my 18V Ridgid batteries.

For this design, I was inspired by donucat's design for Ryobi 18V batteries. I went with a similar approach that uses a purchased USB power socket and a rocker switch to avoid battery drain while in storage.

For the Ridgid battery adapter, I completely remodeled itnaanti's adapter design, adapting the printability improvements made by MortarArt and designed a new cover incorporating the Ridgid logo. itnaanti has a clever approach for making the battery contacts from scratch, but I chose to purchase a knock-off Ridgid battery connector from AliExpress and harvested the terminals from it since the housing it came with (3D printed by the way) wouldn't work with my design. The scratch-built terminals might still fit in this design as well. I chose to use brass threaded inserts since I would be disassembling and reassembling it several times and I didn't want to strip plastic threads. I also didn't want to hassle with installing hex nuts that might fall out during assembly.

It's a little fiddly to get the terminals installed into the holder pieces and then attached to the adapter base, but once that's done, the rest is pretty simple.

Bill of Materials:

3D Printed Parts:

(1) Ridgid Adapter_Base
(1) Ridgid Adapter_Cover
(1) Terminal Holder_Btm
(1) Terminal Holder_Top

Purchased Parts: (links are provided for the parts I used)

(1) 12/24VDC USB Power Socket

Make sure the socket can handle the voltage range of the battery (~18-20VDC in this case). The socket I used can handle 9-32VDC.

(1) Rocker Switch

(1) Ridgid/AEG Battery Connector

I used the terminals and wires and discarded the plastic housings.

(6) M3 3x4x5 (4mm long) Brass Thread Inserts
A cordless USB rechargeable soldering iron works great for installing the inserts. I recommend inserts with angled knurl rather than straight knurl for better grip in the plastic.