Charging VRLA products

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. 

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. 

Existing Charging Methods Applied to VRLA Products... 

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]. 

As noted earlier, new VRLA batteries behave very much like flooded products in overcharge for a period of time the saturation level is so high (95% +) that gas paths between the plates are not created during overcharge, and thus the plates finish charge independently ... 

Given the foregoing, a series of requirements for optimized charging of VRLA batteries can be formulated. It should be noted that this approach will be necessary earlier in life and more obviously effective with thin-plate products. Thick-plate cells. 

To complicate the situation even more, many of the properties of an AGM battery are already exhibited by modern, totally maintenance-free batteries with liquid electrolytes. This is particularly true for starter batteries as they are only expected to have a service-life of about 2000 h, which is considerably less than one-tenth of that which industrial battery manufacturers claim their products achieve when used in constant-voltage, float-charging applications. As a result, a VRLA battery will be used in vehicles with conventional electric power systems only if its advantages over a flooded battery are really needed. These include the following. 

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. 

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