Most modern MPPT (Maximum Point Power Tracking) smart solar charge controllers use 4-stage battery charging process. Battery life is prolonged and therefore keeping them at optimal performance at all times. Smart Chargers can also protect the battery from being overloaded, short circuits, high input voltages, over discharge and temperature variations.
The 4 Battery Charging Stages
Bulk Charge – the battery is in 100% power bulk charge mode.
Absorption Charge – the battery has completed the bulk charging and is in absorption state of charge.
Float Charge – the battery has completed charging and is in maintenance float charge.
Equalize Mode – cell voltage is raised to make the battery gas and level the voltages.
Bulk Charge Stage
In the bulk charging stage the battery is not at 100% full capacity. The battery voltage has not yet reached the Absorption Voltage point. The smart solar charger will deliver 100% of all available power to recharge the battery.
Absorption Charge
When the battery has completed the bulk charge the battery regulator will enter the float charge mode. The Absorption Voltage set point configured in the controller has been reached. At this point, constant voltage regulation is used to maintain the battery voltage at the set point.
This will prevent the battery from overheating and producing excessive battery gas. The battery will obtain a full state of charge at the Absorption Voltage set point.
The battery will remain in the Absorption Charge Stage for typically 120 – 150 minutes depending on the battery type and age.
Float Charge
The battery is now fully charged and the voltage is reduced to the Float Voltage set point. There is no more battery chemical reactions at the stage and all charging current is dissipated as heat and gassing of the battery.
Heat and gassing is reduced and provides a very low rate of maintenance charge. This stage protects the battery from long term overcharge.
Equalize Stage
This is a periodic boost charge required by certain batteries. The electrolyte is excited and stired while leveling out the cell voltages to complete the chemical processes.
The battery voltage is raised above the Absorption set point, so that the electrolyte in the battery starts to gas. This Equalization stage is typically completed every 30 days.
Temperature Compensation
Smart Solar App from Victron 
Solar Voltage and Current Graphs Battery Daily Charging Info
Most modern battery solar regulators have an external temperature sensor so that the battery charging voltages and times can be adjusted. The regulator will compensate for maximum efficiency and battery condition for varying temperatures.
