The four stages of RV battery charging.
This article will talk about Flooded and AGM. There are 4 main stages of battery charging: Bulk, Absorption, Float and Equalize. I will start out letting you know that your converter charger that came with your RV is not capable of charging your battery optimuly!
The first stage, Bulk, will get the battery the most amount of current and charge, approximately 85% State of Charge (SOC). This is the most efficient stage of charging the battery. This could take about an hour, it all depends on the SOC or the amount of room in the battery.. Typical Flooded will accept a c/20 charger=20 amps per 100AH battery during the Bulk stage. I have Lifeline AGM and they will actually take 5C charging, so 500 amps per 100AH! This will shorten the charging profile if you have the charging power.
The second stage, Absorption, is a constant voltage at say 14.4 volt. The amperage will continue to fall until the charge is 100% complete. Most chargers will time the Absorption stage according to the SOC at the start of the charge. This stage can take 2-6 hrs depending on SOC and battery manufactures specs. At the end of this stage your battery is completely charged!
Typically a battery is defined as fully charged when the resting voltage is >12.6 volts. Resting voltage is defined as 24hrs with the battery disconnected or with no loads or charge applied.
The third stage, Float, is to maintain the battery charge. This is typically a 13.6 volt trickle charge to compensate for any self discharge of the battery, and supply power for small loads on the system. These small loads could consist of a propane fridge, thermostats, propane sensors or a break away battery being charged. If you have a big enough load on the system, the charger will cycle back to Bulk stage.
The fourth stage, Equalization, will reduce the sulfation on the battery plates by ‘overcharging’ them allowing the battery to be more efficient. This should only be performed by someone who is very familiar with this process! Flooded batteries should be equalized every 2-8 weeks. This cycle will cause gassing and could boil some acid out as well. You will need to measure the specific gravity of the acid during the process to determine when the cycle is complete. Now with AGM batteries the equalization charge is used as a recovery tool when they have a noticeable capacity loss, however this will not apply to all AGM batteries. You always should start at your battery manufacturers website your exact battery.