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Inverter Battery Maintenance Tip: How to Perform an Equalization Charge on Your Inverter Batteries.

Updated: Jul 7

Inverter Batteries

Most inverter batteries are ‘deep-cycle’ or ‘lead-acid’ batteries. [Read all about inverter batteries here.] In other words, these type batteries are ‘flooded cells’, that is they are batteries that convert wet acid energy directly to electrical energy. The primary components of a flooded cell battery include.


Electrolyte. The electrolyte in most wet-cell batteries is sulphuric acid diluted with distilled water. Inverter batteries are mostly wet-cell batteries. The two types of lead-acid batteries that use an acidic electrolyte are wet cell and sealed. Wet cell use liquid electrolyte; sealed batteries use either a gel or liquid electrolyte absorbed into fibreglass material.


Terminals. The terminals are the pure lead at the negative side and the PbO2 on the positive side both constructed as ‘plates’. With acid electrolyte and lead plates, wet-cell batteries are therefore known as ‘lead-acid’ batteries.


Separators. Separators between the positive and negative plates prevent short-circuit through physical contact, mostly through dendrites but also through shedding of the active material. Most separators are made of rubber. They are more stable in battery acid and provide valuable electrochemical advantages that other materials cannot.


Sulfation and Stratification

Constantly recharging lead-acid or deep-cycle inverter batteries with a charger using a constant voltage or a fixed charge algorithm can, over time, cause the acid in the electrolyte to separate from the water and settle at the bottom of the battery.


In flooded or wet cells, the charging process produces sulphuric acid which is denser than water. Over time layers form in the electrolyte which means that the acid becomes concentrated at the bottom of the battery. Otherwise called ‘stratification’, this can cause damage to the bottom area of the battery plates. An equalizing charge is meant to help reverse the stratification effect.


Also, sulfate crystals accumulate around the plates. Otherwise called sulfation, this too reduces the overall capacity of the battery. All lead acid batteries will accumulate sulfation in their lifetime as it is part of the natural chemical process of a battery. But, sulfation builds up and causes problems mostly when;


  • A battery is overcharged

  • A battery is stored above 75 degrees

  • A battery is stored without a full charge

  • And a battery is not in use for a long time.


Sulfation is the primary cause of battery failure. Extreme cases of sulphation can render a battery unserviceable.


To prevent stratification and to remove the accumulate sulfate crystals on the battery plates and thus, extend battery life and increase performance, it’s important to regularly perform an equalizing procedure to your batteries.


What Is An Equalizing Charge?

An equalizing charge is a deliberate or ‘controlled’ overcharge of the battery. It is a recommended part of the overall battery maintenance procedure.


The purpose is to reverse sulfation, that is, remove sulfate crystals from the battery plates and also restore the balance in the electrolyte. And thus, improve the performance of the battery and extend its life.



How Does An Equalizing Charge Work?

An equalizing charge is the addition of an extended charge at the end of the normal charging process. When this is done, the extended charge removes the sulfate coating around the battery plates allowing all the surface area of the plates to interact fully with the electrolyte in the battery.


It causes the electrolyte to bubble or ‘gas’ and this mixes up the acid and water and distributes it evenly throughout the cell. Equalisation generates hydrogen and oxygen gases and the bubbles that are formed stir the electrolyte.


When Should An Equalizing Charge Procedure Be Performed On A Battery?

Many experts and manufacturers recommend that batteries be equalized periodically, ranging from once a month to once or twice per year.


A more precise method is to apply a fully saturated charge and then compare the specific gravity readings (SG) on the individual cells of a flooded lead acid battery with a hydrometer. An equalization is to be performed if the SG difference between the cells is 0.030.


However, generally, a reduced battery performance is often an indication that your battery may be in need of an equalizing charge.

Also, a battery that regularly reaches a full charge will need an equalization charge less frequently compared to a battery that is not used as often.


Step By Step Procedure for Equalization

The following procedures are recommended

  1. Identify the type of battery. In other words, make sure your battery is a flooded lead-acid type. The equalization process is recommended only for flooded batteries. Nevertheless, though they can be equalized, equalizing VRLA and other sealed batteries involves guesswork and this procedure is not recommended. Also make sure that your charger has an equalizing mode. Not all chargers have an equalizing charge mode. If not, the procedure may vary a little.

  2. Disconnect all appliances. Because the battery is being overcharged, appliances still connected to it may be damaged.

  3. Connect the charger and perform a normal charge. Some chargers have an automatic equalization mode. In this case, do not disconnect the charge so that it can charge long enough to complete equalization.

  4. If the charger does not have an automatic equalization mode, wait till after the normal automatic charge is complete then restart the charger by disconnecting it and reconnecting. The charger will restart and extend the charge time by 1-3 hours.

  5. Correct equalization will cause gassing and vigorous bubbling of the electrolyte. Note this.

  6. Also take specific gravity readings every hour.

  7. The process is complete if the specific gravity reading becomes constant and no longer increases during the gassing time. If the charger terminates the charge automatically, before the hourly specific gravity readings become constant, then restart the charger and continue the process until specific gravity readings become constant.

  8. Top up the water level of the battery. Water is often lost during this process, it is recommended that the water level is topped up after the charge. Distilled water is to be used.

  9. Finally, depending on the degree of sulfation and the battery type, the process could take hours.

Be Mindful Of These Safety Tips When Performing An Equalizing Charge.

  1. Most importantly, the process must be attended to in person. Do not initiate it and leave. Keep a close eye on the process.

  2. Only perform this process if you can do so in a safe manner and have the appropriate equipment.

  3. Overheating of the battery during the process can cause damage. As the battery heats up, hydrogen is emitted. This venting is normal and should not be considered a malfunction. However, the hydrogen gas that is being emitted is very flammable. If the room is not properly ventilated and the battery gets too hot, the hydrogen could explode. Therefore, It’s a good idea to keep the room cool and ensure good ventilation before you get started. (Hydrogen only has to reach a concentration of 4% before it becomes explosive so it’s best to have the room properly set up before you start.).

  4. In conclusion, the equalization procedure is one of the many maintenance tips for inverter batteries. Read about the others here. While the process can be tedious, time-consuming and as far as the hydrogen gas goes, very smelly, it will help maximize battery life and increase their performance. This will help lower operation costs.

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