VRLA Products

As noted earlier, charging methods used for VRLA batteries have largely been similar or identical to those developed for flooded counterparts. This is natural, as both are lead-acid chemistries and most battery companies experience began with flooded versions. In fact, these traditional approaches work very well for VRLA products early in life, when their highly saturated conditions closely approximate flooded lead-acid environments. 

VRLA products can experience thermal runaway due to the high finishing currents available, as with CV charging. 

The important design difference between VRLA and flooded lead-acid batteries is the partially saturated condition of the plates and separator in VRLA products. As noted earlier, the diffusion rates for oxygen and hydrogen are lO times greater... 

Clearly, this is unacceptable. This is what must be dealt with, however, in properly charging VRLA products. If this thermodynamic fact is not addressed, VRLA products will fail prematurely, not due to dry-out or grid corrosion, but due to insufficient recharge of the negative plate. 

Existing Charging Methods Applied to VRLA Products... 

In practice, some form of iterative process is best used to obtain maximum eyele-life with VRLA products a fixed algorithm will eventually fail, even for thiek-plate products. The simplest approach is to apply a step-wise inerease in eharge factor once the performance of the battery has been characterized, e.g., 1.05-200 cycles,... 

Clearly, Cl may not be a universal algorithm, but it would be interesting to see what cycle-lives could be achieved with this procedure on thicker-plate VRLA batteries, where the oxygen cycle is not as active as in the Optima and Genesis products. It should be noted that each product may require a unique approach, as design dictates maximum current levels and recharge times in VRLA products. This has been demonstrated in the Cominco ALABC work on fast charging of Optima (thin-plate) and Delphi (thick-plate) batteries [61]. 

Due to the incorporation of VRLA products into such new applications as HEV and photovoltaics/wind/hydro-electric energy conversion, or RAPS (remote-area power sources), the development of cycling algorithms involving a relatively narrow SoC window has emerged. While it is beyond the scope of this review to cover this topic in great depth, a general overview will be presented. 

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