FIGURE. The recombination battery is one of the most recent advances in the automotive battery.
A recent variation of the automobile battery is the recombination battery. The recombination battery is sometimes called a gel-cell battery. It does not use a liquid electrolyte. Instead, it uses separators that hold a gel-type material. The separators are placed between the grids and have very low electrical resistance. The spiral design provides a larger plate surface area than that in conventional batteries. In addition, the close plate spacing results in decreased resistance. Because of this design, output voltage and current are higher than in conventional batteries. The extra amount of available voltage (approximately 0.6 V) assists in cold-weather starting. Also, gassing is virtually eliminated and the battery can recharge faster.
FIGURE. Construction of the recombination battery cells.
The following are some other safety features and advantages of the recombination battery:
- Contains no liquid electrolyte. If the case is cracked, no electrolyte will spill.
- Can be installed in any position, including upside down.
- Is corrosion free.
- Has very low maintenance because there is no electrolyte loss.
- Can last as much as four times longer than conventional batteries.
- Can withstand deep cycling without damage.
- Can be rated over 800 cold cranking amperes.
Recombination batteries recombine the oxygen gas that is normally produced on the positive plates with the hydrogen given off by the negative plates. This recombination of oxygen and hydrogen produces water (H,0) and replaces the moisture in the battery. The electrolyte solution of the recombination battery is absorbed into the separators.
The oxygen produced by the positive plates is trapped in the cell by special pressurized sealing vents. The oxygen gases then travel to the negative plates through small fissures in the gelled electrolyte. There are between one and six one-way safety valves in the top of the battery. The safety valves are necessary for maintaining a positive pressure inside of the battery case. This positive pressure prevents oxygen from the atmosphere from entering the battery and causing corrosion. Also, the safety valves must release excessive pressure that may be produced if the battery is overcharged.
Absorbed Glass Mat Batteries
A variation of the recombination battery is the absorbed glass mat (AGM) battery. Instead of using a gel, they hold their electrolyte in a moistened fiberglass matting. The matting is sandwiched between the battery’s lead plates. The plates are made of high-purity lead and are tightly compressed into six cells. Separation of the plates is done by acid-permeated vitreous separators that act as sponges to absorb acid. Each cell is enclosed in its own cylinder within the battery case. This results in a sealed battery.
During normal discharging and charging of the battery, the hydrogen and oxygen sealed within the battery are captured and recombined to form water within the electrolyte. This process of recombining hydrogen and oxygen eliminates the need to add water to the battery. Typical of recombination batteries, the AGM battery is not easily damaged due to vibrations or impact. AGM batteries also have short recharging times and low internal resistance, which increases output.
All recombination batteries are classified as valve regulated batteries since they have oneway safety valves that control the internal pressure of the battery case. The valve will open to relieve any excessive pressure within the battery but at all other times the valve is closed and seals the battery. A Valve-Regulated Lead-Acid (VRLA) battery is another variation of the recombination battery. As the name implies, these are lead-acid batteries. Within the VRLA battery, the oxygen produced on the positive plate is absorbed by the negative plate. This causes a decrease in the amount of hydrogen produced at the negative plate. The small amount of hydrogen that is produced is combined with the oxygen to produce water that is returned to the electrolyte.
The VRLA uses a plate construction with a base of lead-tin-calcium alloy. The active material of one of the plates is porous lead dioxide, while the active material of the other plate is spongy lead. Sulfuric acid is used as the electrolyte. The sulfuric acid is absorbed into plate separators made of a glass-fiber fabric.