MPPT stands for Maximum Power Point Tracking. It observes and regulates the energy going from the solar panel to the batteries. Solar panels have a variable output depending on the light available. The devices can match the panel’s voltage with the battery voltage to maximise charge efficiency.
PWM stands for Pulse Width Modulation. The devices can be explained as electrical switches between batteries. It can be quickly switched on and off. Which allows the desired voltage to be obtained to charge the batteries.