Need help in making an automatic battery cut-off switch
A simple way is shove a MOSFET in series with the Solar Panel, and use a comparator to toggle it on and off. A very simple way to show that would be:







simulate this circuit &ndash; Schematic created using CircuitLab

This is incredibly simplified but it should provide a good starting point to work from. You can set your Vref to whatever you want, and monitor the battery voltage so when it hits a certain threshold, the comparator toggles the MOSFET, which in turn will switch the Solar Panel on and off.