Recombination batteries

Covers for the battery designs in Figures 1 and 2 are typically molded from materials identical to that of the respective case, and vent plugs are frequentiy made of molded polypropylene. Other combinations are possible, eg, containers molded of polyethylene or polypropylene may be mated with covers of high impact mbber for use in industrial batteries. After the cover is fitted over the terminal post, it is sealed onto the case. The cover is heat bonded to the case, if it is plastic it is sealed with an epoxy resin or other adhesive, if it is vulcanized mbber. Vent caps are usually inserted into the cover s acid fiU holes to faciHtate water addition and safety vent gasses, except for nonaccessible maintenance-free or recombinant batteries. In nonaccessible batteries, the vent is fabricated as part of the cover. 

Two lypes of batteries having immobilized electrolyte systems are also made. They are most common in consumer applications, but their use in industrial and SLI applications is increasing. Both types have low maintenance requirements and usually can be operated in any position. They arc sometimes called valve regulated or recombinant batteries because they are equipped with a one-way pressure relief vent and normally operate in a sealed condition with an oxygen recombination cycle to reduce water loss. 

Battery Council International, Battery Technical Manual Test Methods for Recombinant Battery Separator Mat (RBSM) 5/93 (1993). 

There are additional advantages with recombination batteries. For example, topping up with water is not necessary over the whole life of the battery, and the battery can be designed to survive a 30-day short-circuit test and, after recharge, have virtually the same capacity as before the test. Due to a marked reduction in water decomposition, there is only a small release of hydrogen gas and a low rate of self-discharge. Many studies of VRLA batteries have been published in recent years some examples are given as Refs. [2-14] (see also Chapter 1). 

As noted earlier, a gel cell is a recombinant battery. This means that the oxygen that is normally produced on the positive plates in all batteries recombines with the hydrogen given off by the negative plates. The combination of hydrogen and oxygen produces water, which replaces the moisture lost in wet-cell batteries. Therefore, the battery is maintenance free, because it never needs water to be added. 

---