What are the compulsory tasks of a charge controller for a lead acid battery?

Question

Solar charge voltage regulators should coordinate the charging process of a battery. Suppose that I would like to design a very basic charging regulator controller with the following specs:

1. The battery charged is a 12V 12Ah lead acid battery.

2. The power supply is a 12V 10W solar panel.

3. During the day the battery is not used.

What are the minimum requirements and specs that are required? At the top of my mind I thought of the following:

1. Over voltage protection (the charging should stop when Vbattery > Vmax)
2. Over current protection (the current should be less than the maximum allowable by the battery) but this seems not to be an issue since the PV module is just 10W 12V.

If you need a battery for reference, then just take this one.

Answer 1

The bare minimum requirements I would set at:

• Undervoltage protection. Do not charge is battery open cell voltage is too low.
• Overvoltage protection. To protect the charger.
• Timeout. When during charging the voltage does not rise as expected.

But you can do many more things:

• You can follow the proper lead-acid battery charging profile. Source

• You can measure battery temperature, and adjust charging rate respectively.

• You can give a battery end-of-life warning.
• You can measure the energy going in/out of the battery. Giving a pre-warning: "please charge", and disconnect if it gets very low. In order to preserve the battery. Batteries last longer when not depleted often.

Answer 2

When the solar panel's voltage drops below the battery's voltage, current would flow from battery to the solar panel.(Because current flows from higher potential to lower potential).

A diode whose anode connected to the solar charger's output, cathode connected to the battery's +ve terminal would prevent the solar panel from getting damaged by preventing this current flow.

^{simulate this circuit – Schematic created using CircuitLab}