Flooded batteries

Flooded battery — A battery (or a cell) containing an excess of electrolytic solution (in contrast to starved electrolyte batteries). Usually relevant to rechargeable -> lead-acid and -> nickel-cadmium batteries. Flooded battery design is typically applicable for heavy duty batteries, equipped with a vent valve that releases pressure buildup due to gas evolution. The excess electrolyte affects more sturdy batteries to become less susceptible to damage due to overcharge. In addition, the thermal conductivity of the electrolyte affords more efficient heat dissipation and thus higher -> power densities. 

Starved electrolyte battery — A -> battery with minimum amount of -> electrolyte. The electrolyte in starved electrolyte cells or batteries exists in the porous structure of the - electrodes and absorbed in the separator, so it contains little or no free fluid electrolytic solution. This type of batteries is used in certain constructions of sealed - lead-acid and -> nickel-cadmium batteries that rely on gas diffusion and recombination on the electrodes during charging or overcharging in order to maintain maintenance-free conditions, and to suppress pressure buildup. Starved electrolyte batteries benefit from larger - energy density due to the reduced amount of electrolyte. This design may suffer from poor heat dissipation compared with -> flooded batteries, thus for high power applications this point has to be taken into account. 

With the aid of these several measures, substantial service lives can be obtained from flooded batteries in their various applications. The drive towards increased... 

K , while the corresponding value for flooded batteries is slightly above The difference is due mainly to the additional electrolyte in flooded... 

In contrast to most conventional separators for flooded batteries, separators for gel batteries have ribs positioned not only towards the positive plate, but also towards the negative plate in order to facilitate the gel-fllling process. For batteries with pasted positive plates, the separator is usually laminated with a glass fleece, which protects the positive plate against shedding, especially in cycle applications. Although this surface fleece stabilizes the active material, the present design of gel batteries cannot prevent completely the expansion of the positive material and the occurrence of PCL-2. The most important characteristics of separators used in gel batteries are listed in Table 7.2 (adapted from Ref. 12). 

It is notable that, of the 17 BESSs listed in Table 10.1, the majority employed flooded batteries. Only four are known to have used VRLA batteries, namely, the SDG E, Johnson Controls, GNB-Vernon, and Metlakatla systems. The performance of the SDG E (gel) and Johnson Controls (gel) batteries appears to be not well documented in the literature. The systems date from 1992 and 1989, respectively, and the SDG E system was taken out of service about two years later. The BESS systems at Vernon and Metlakatla had AGM-type batteries. Both are still in service and seem to be performing well. These batteries date from 1996 and 1997, respectively. 

Cost. Although VRLA is expected to settle at about 25% higher cost than flooded, there may be some applications where this cost increment is acceptable. High-capacity, deep-cycle applications are one case where low-cost automotive flooded batteries cannot usually match VRLA performance, but where alternative batteries that cost an order of magnitude more are not feasible. In this comparison, the lower cost of VRLA relative to Ni-MH or lithium batteries must be weighed against the higher mass and lower reliability of VRLA, but should the mass and life be within... 

The service-life of a conventional flooded battery under the harsh operating scheme in taxis, i.e., extended periods of standstill with lights and other equipment switched on, is only 6-12 months in Europe. In high-temperature climates, this may be even shorter. Taxi operation generates much more cycling of the battery than is found for the same type of car in private use, and this results in a tremendous reduction in battery life. Field tests with AGM batteries have shown an extension of taxi-duty life by a factor of 2 3 over flooded batteries. Therefore, a major European manufacturer has equipped all new taxis with AGM batteries since 2001. 

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. 

The main benefits of AGM batteries in present-day automotive applications, as compared with flooded battery designs with the same outer dimensions, are (i) higher power capability (ii) improved cycling capability, e.g., as in taxis ... 

Lead-acid batteries were first used in stationary, stand-by applications more than 130 years ago [1]. For a long period of time, only flooded lead-acid batteries were used. Nowadays, UPS and telecommunications applications use valve-regulated batteries. Large, utility-scale applications such as load levelling continue to use flooded batteries, but it seems that, increasingly, valve-regulated batteries are chosen even for these applications. 

In summary, it seems that there is a rapidly increasing market for large batteries in a variety of utility applications. So far, this has mainly been a market for flooded batteries, but it is likely that the valve-regulated battery can replace the flooded battery in utility applications in the same way that it has replaced them in UPS and telecommunications applications. 

Flooded batteries operated in RAPS systems require water maintenance on a regular basis. Unfortunately, it is not uncommon for owner/operators to neglect this tedious task. This situation can affect the performance of the system and can ultimately result in premature failure of the batteries. Problems can also arise if the water used for topping up contains excessive amounts of impurities. For example, the presence of chloride ion leads to enhanced corrosion of the positive grids [11]. Also, some RAPS systems are located in areas where access is very difficult, e.g., microwave repeater stations on the tops of mountains. Hence, the cost of maintaining flooded batteries can be very high. 

Electrolyte stratification has been responsible for the failure of many flooded battery banks. In simple terms, this phenomenon can be defined as a build-up of higher strength acid at the bottom of the battery. Stratification occurs because sulfuric acid has a higher density than water and, when formed during the charging process, will sink to the bottom of the battery container. Such behaviour results in a decrease in battery capacity due to uneven utilization of the active material [12]. Moreover, if the resulting concentration gradient is allowed to remain for extended periods, premature failure of the battery can occur. 

A further operational disadvantage of VRLA batteries is that the relative density of the electrolyte cannot be measured unless the battery is disassembled. Hence, voltage and current data are the only parameters that can be used to evaluate the condition of the batteries during operation. In addition, VRLA batteries are not available in a dry-charged condition. As a consequence, they have a shelf-life of only two years. (Note, dry-charged, flooded batteries if sealed airtight can have a shelf-life of > 5 years.)... 

There will also be a responsibility to recycle the VRLA battery in an as environmentally sound and efficient manner as now occurs with conventional flooded batteries. 

Flooded batteries (with high-Sb grid alloys) — they require regular maintenance. 

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