Protective enclosure to keep components on the board from damage. In my application, I an using the board to provide a 9V supply with enough current output to run my QRP-Labs QMX+. I also use it to charge my Xiegu X6100 when I don't have another power source available.
I put a zip tie on the wires behind the opening as a strain relief to help the solder connection not fatigue. M2.5 socket head screws fit with a little clearance.
Battery board on Amazon does not include batteries. Is intended to work like a battery backup for 9V electronics (like wireless router), does drain batteries while sitting. Remove batteries during long periods of disuse. I usually like to leave on the charger day before an outing. 18650 batteries can be hazardous if not disposed of properly. Check with your local recycling centers for disposal. Home Depot may have a battery disposal bin.
Screws I used on Amazon, although a little shorter would be a lot less tedious to put in.
The author marked this model as their own original creation.