Wanted to make a portable Power source for the CPAP on camping trips, and already use a ton of Ryobi One Plus devices (lights, radio, etc.) when camping.    Leaf spring contacts work perfectly as described in the source build. The battery contacts are set up in parallel for the added amperage. Soldered on a 24v to 12v dc step-down transformer. And added a cigarette lighter plug and 2 USBs as well as a 2post Flat connector.