This is a battery holder for two 18650 batteries which keep the overall look and operation cleaner by hiding the soldering, joints and wire connections. I needed a practical way of installing my batteries which can be placed into a holder but need to be soldered so they could be easily fixed on top of any surface with screws to the holder.
You will need to use a specific type of battery holder as shown in the pictures, but it's a common model. You can get it easily from online stores, such as Aliexpress.
I was inspired by a similar battery holder for one battery: https://www.thingiverse.com/thing:2744505