Desoldered wires
Research potential solar panels to purchase
Test to see if the solar panel works on gateway
Drained one of the batteries
Switched the board to male headers and changed the wires connected to the sp215 into female headers
When cutting the wires that are connected to the sp215, it was found that the colors of the wires didn't match.
For future purpose, Red is the signal, Black is the +5V, and the one with no sheathing is the ground.
The reason why the battery stops sending signals despite having voltage is because the Arduino needs a minimum battery voltage of 3.3V in order to send signals.