9V battery cells have this connector that is basically reversible. This connector consists of one female and one male pin that is the same on both the battery and the receiving connector so we can salvage them from the empty cells to make new connectors for our projects.
I've recently created a video and an Instructable where I'm showing the process of making them so you may want to check them out.
Additionally, these batteries are usually constructed out of 6 AAAA 1.5V cells so if you are in a need of such cells for a project you know where to get them.
Depending on the battery manufacturer, the cells inside can be welded together but in my case, they were just press fitted together with a rubber gasket, so once I opened the case everything just fall down and the part that we are most interested in was not soldered or welded to anything.
If you liked this project, please check out all of my other ones and feel free to subscribe to my YouTube channel for more similar projects.