VRLA batteries technology

Two VRLA battery technologies are currently predominant, i.e., absorptive glass mat (AGM) and gel designs. In the former, the AGM immobilizes the electrolyte and simultaneously functions as a separator. In gel batteries, the acid is immobilized by means of fumed silica, and an additional separator is required to fix the plate distance and to prevent electronic shorts. 

Table 7.3. Characteristics of state-of-the-art separator technologies for VRLA batteries.

Automotive applications of batteries have developed well beyond the original crank requirement of Kettering and now include a continuum of function, from the basic crank and engine control modules all the way through hybrid and pure electric drive vehicles. Each of these applications has its own attributes and needs, so it is understandable that VRLA (or any battery technology) may be more suitable for one application than for another. 

Under low-temperature conditions, the battery will rarely achieve a full SoC. In fact, the specifications laid down in the various standards do not represent the duty the SLI battery has to serve in a modern automobile. For advanced vehicle electrical systems, which may be a motivation for new battery technologies like the VRLA, it is essential to know the expected operating condition in order to evaluate alternative energy-storage technologies. 

Many questions about 36-V, VRLA batteries remain yet unanswered, e.g., production reliability, need for individual-cell charge control in the 18-cell string, and the anticipated heat build-up during intensive cycling operation. Battery technology, however, is not expected to impede the introduction of the 42-V PowerNet — a marked contrast to the plans to introduce EVs as a mass-product in the 1970s and 1990s. 

In summary, the VRLA battery will claim a significant portion of the future automotive battery market. Due to cost considerations, conventional designs will also continue to be used. On the other hand, since lead acid technology is limited in some applications, other electrochemical systems will also gain a share of the market. 

Traditionally, flooded lead-acid batteries have been the technology of choice for use in RAPS systems. During the last 10 years, however, there has been a considerable shift towards VRLA batteries. The main driver for this change is the low maintenance requirement of the latter technology. This and other important issues are discussed in the following sections. 

Fig. 17.2. Variation of cycle-life with depth-of-discharge of a spiral-wound VRLA battery (Courtesy of Exide Technologies).

Much of the recent advancement of VRLA technology has been achieved through a co-operative research effort under the auspices of the Advanced Lead-Acid Battery Consortium (ALABQ. The main effort has been directed towards the development of VRLA battery systems for new-generation road transportation — electric and hybrid electric vehicles — that will reduce fuel consumption and lower emissions. The progress gained in this endeavour will ultimately also benefit the enormously important markets in telecommunications and remote-area power supplies. 

This volume presents a detailed account of recent advances in the science and technology of VRLA batteries. The expert contributors are from organizations which have either been members of, or contractors to, the ALABC. In editing the contributions, we have aimed to unify the style of the volume as far as possible, but have allowed a Kttle overlap between those chapters where there is a natural interaction between topics. It is hoped that this work will constitute a sound exposition of the present status of VRLA batteries, and will provide a resource that will enable technologists to dehver products with performances that surpass the requirements of the major markets. 

There are two basic technologies employed in VRLA batteries depending on the type of separator used and the electrolyte state ... 

This report analysed four units in the field, as compared with VRLA batteries in terms of both performance and economics. The results, in this study, showed a saving of 27% using the fuel cell technology (Table 5.3). 

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