The charge controller is used to connect a solar panel to a 12 volt lead acid battery, it regulates the charging of the battery and allows the battery to be charged up to a preset voltage. This prevents the battery from over-charging and boiling off electrolyte.
The low voltage disconnect is used to connect a load to the same 12 volt lead acid battery, the LVD acts as a smart switch, it auto disconnects the load if the battery voltage falls below a set point.
When used together, these circuits keep the battery operating within normal voltage limits which greatly extends the life of the battery. The circuit board was designed to be split into two independent circuits, that is why there are two connections to the battery.