I recently purchased a solar electric fence energizer, specifically the Patriot PS5. After it had been sitting in the sun a while, I noticed the battery was making a "gurgling" noise, which according to my research means the battery is overcharging. Upon opening the unit, I noticed that there was no protection circuitry whatsoever between the solar panel and the battery.
The battery is a 4 V SLA battery, and the solar panel can reach up to 8 V on a sunny day with no load. The solar panel, battery, and the rest of the electronics for the energizer are all connected in parallel.
My question is, what is a simple way I can modify the circuit to prevent overcharging of the battery? Also, is the 3-step process recommended by Battery University necessary in this case, or will a simple voltage-based cutoff work?
I designed the circuit below for this purpose, but I'm not sure if it will work or not, and it seems somewhat over-complicated. It uses a diode-based voltage reference and an op-amp to determine if the battery voltage is above a certain level, and shuts off current flow to the battery if it is.
I'm fairly new to this, so I'm sorry if the schematic is poorly laid out. Any feedback would be great. Thank you!