Good battery chargers or charge controllers/regulators will charge your batteries in stages depending on how much charge is left in the battery. Three or four stages are the most common, this article will explain how a four stage battery charger works. We will also explain why it is important that you use the correct program settings in your charge controller.
How 4-stage charging works
Stage 1 (bulk) – If the batteries are at a lower state of charge, usually less than 80%, this is the first stage. When in the bulk stage, the solar panel or generator will put as many amps into the batteries as possible. This is the high speed charge stage, the higher the amperage, the faster the charge.
Stage 2 (Absorb) – when the batteries reach the “Absorption Voltage” (this number varies depending on the program settings, but generally around 14.5 volts for lead-acid batteries), the charger or regulator should go into the Absorption stage . At this stage, the batteries are kept at the voltage set by the program. The amperage going into the batteries is lower at this stage and the batteries charge more slowly. The absorption stage can end after a set time has passed or when the number of amps coming in drops below a threshold. All this is decided by the configuration of the charging program.
Stage 3 (Float) – when the absorption stage ends, the charge controller will lower the voltage to a value defined by the program and the float stage will begin. This stage will activate when the battery reaches 100% charge.
Stage 4 (Equalization) – this stage will actually overcharge the battery. But it only comes on periodically to override the Float stage. This is optimal for lead-acid batteries and will extend battery life and performance.
The importance of using the correct load settings
Using the correct program settings for your battery charger or charge controller will extend its life and performance. To find out what the correct settings are, you will need to check what type of battery you have. Of course, it will also depend on the type of charger you are using. For example, a deep cycle battery charger can charge deep cycle batteries. You can read more about the difference between a deep cycle battery and a regular car battery here. But deep cycle batteries have several subtypes. So depending on what subtype you want to load, you need to select the appropriate program for it.
You should also be aware that there are battery types that do not even need to be charged in 4 stages, such as lithium-ion batteries. Lithium-ion batteries should not be overcharged, so in this case it is even more important that you select the correct charge setting or the battery could be damaged.