My charger, the Luna Mate 52V Charger Advanced 300W Ebike Charger says on the top to never leave the battery unattended during charging but I can't hang around and watch the thing, that's ridiculous,

So I have an old ammo case hanging around
I saw the Luna Ammo Cases, just drill a couple of vent holes into it and a hole for the charger cable
What size vent holes should I drill in it and how many ??