I see an OOOPS not sure you know this or not but perhaps you fixed it already. Years ago we used wet cell batteries for our flight boxes. When charging they emit dangerous explosive gasses that need vented off hens the slots on the front of the box which also dissipates heat from high use and charging, heat is the enemy of all batteries. If you put the cover on yours it will not vent properly now. However most of us use dry cell batteries now that require little gas venting anyway. So it’s most likely not a huge problem but keep the cover off during charging so the heat can escape.