The circuit board measures only 0.5” x 1.5 ... They are both inexpensive and BRIGHT! The 12v battery level indicator unit in the photo has no reverse polarity diode and R2 is the calibration ...

It is mainly intended for charging 12V lead-acid batteries ... a solar panel can withstand a short circuit. Therefore, the control does not need current limiting. Float Charge of Lead-Acid Batteries ...