What is Captive Electrolyte Battery?


A captive electrolyte battery is a battery with an immobilized electrolyte that has either gelled or been absorbed by a substance. Sulfuric acid is immobilized in captive electrolyte batteries either by gelling the acid or by utilizing an absorptive glass mat. Both are frequently seen in maintenance-free sealed lead acid batteries because they both have lower gassing than flooded lead acid batteries.

Gelling in a lead acid battery means it has been gelled and the electrolyte can be immobilized by silica gelling the sulfuric acid. The gelled electrolyte has the benefit of reducing gassing, which makes the batteries low-maintenance. Additionally, because the electrolyte is gelled, there is less possibility of sulfuric acid spilling because stratification of the electrolyte does not happen with gelled batteries, negating the need for boost charging.

These gel-cell batteries, however, generally contain lead calcium plates in order to further limit gassing, rendering them unsuitable for deep discharge applications. Another disadvantage is that a gelled lead acid battery’s charging conditions must be more carefully managed to prevent overcharging and battery damage.

Absorptive glass mat batteries, often known as AGM batteries, are a second method that can be utilized to immobilize sulfuric acid. The sulfuric acid in an AGM battery is absorbed in a fiberglass mat that is positioned between the electrode plates.

What are the advantages of using AGM batteries?

AGM batteries provide a lot of benefits, such as the capacity to operate over a wider temperature range, high rates of charge/discharge, and the ability to be deeply depleted without reducing lifetime. These batteries’ main drawbacks are their greater initial cost and the requirement for more meticulously planned recharge schedules.

In conclusion, a captive electrolyte battery is a form of lead-acid battery in which the electrolyte is held in place by an absorbent substance rather than being allowed to freely flow inside the cell. This kind of battery is frequently utilized in applications with restricted space, such as those in the automobile and marine industries.

There are fully sealed batteries available with a gelled (Gel) or absorbed glass mat (AGM) electrolyte. Valve Regulated Batteries is another name for these batteries. Some of the most recent batteries contain internal catalytic recombiners that help to reduce water loss.

What happens when AGM batteries are overcharged? 

If a sealed battery is overcharged to the point of severe gassing, it will vent in order to keep the battery casing from being overly pressurized. In that case, the electrolyte is permanently lost, potentially shortening the battery’s lifespan. By employing temperature correction in the charge controller and charging the battery as directed by the manufacturer, this issue can be minimized or completely resolved.

Typically, lead calcium or lead calcium/antimonial hybrid batteries fall within this category. There is no need to charge the battery to a high enough charge to gas the electrolyte because the electrolyte is captive. Any posture, including upside down, allows for the operation of the battery. The battery still operates at its full capacity since the electrolyte does not flow away from the plates.

Also Read: What is Battery Energy Capacity?

For the correct regulating voltage for their particular battery, the manufacturer should be consulted. These are generally shallow cycle batteries. These batteries’ lifetimes will be drastically shortened if they are discharged by more than 20%. There are some temperature restrictions for these batteries; normally, temperatures between -20 and +50 degrees C should be avoided. Self-discharge rates are extremely low, at least on par with lead calcium batteries.

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