Linden D., Reddy T.B. (eds.) Handbook of batteries
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23.86 CHAPTER TWENTY-THREE
The selection of the proper battery for these types of applications requires a complete
analysis of the battery’s charge and discharge requirements, including the load, the output
and pattern of the solar or alternative energy source, the operating temperature, and the
efficiency of the charger and other system components. Golf-cart-type lead-acid batteries and
modified electric-vehicle designs are widely used in these small stationary energy-storage
systems because they are the least expensive design in commercial production. Maintenance-
free batteries are also being developed for these applications. These batteries (100-Ah size)
can give maintenance-free unattended operation, a self-discharge rate less than 5% per month,
a recharge in less than 8 h, and 1000 to 2000 cycles to an 80% depth of discharge.
23.9.6 Power Conditioning and Uninterrupted Power Systems
DC Power Systems. A new concept in standby power is the DC power system with battery
backup. These power systems include a battery charger (rectifier/charger) which has a suf-
ficient capacity to recharge the batteries at the proper voltage while simultaneously supplying
power to the DC load. In addition, equipment protection and isolation of the line voltage
from the secondary windings of the special power transformer are designed into the system.
Static Uninterruptible AC Power System (UPS). In this power system, a storage battery is
linked to the utility power to provide a continuity of service in the event of an interruption
of the utility power. The continuous UPS system (Fig. 23.54) is illustrative of this type of
device. During normal operation, the AC line supplies power to the static battery charger
(rectifier-charger) which, in turn, ‘‘float’’ charges the battery and, at the same time, supplies
DC power to the static inverter. The inverter, in turn, supplies power to the AC load. A
synchronizing signal (if used) from the AC power line can maintain the phase and frequency
of the inverter output the same as in the power line. This maintains the accuracy of timing
devices such as clocks and recorder charts.
FIGURE 23.54 Schematic of continuous-type uninterruptible power system (UPS).
The voltage regulator within the inverter maintains the AC load voltage constant through-
out the load range as well as during periods of equalizing charge on the storage battery.
Transient and steady-state power-line variations are isolated from the load by the regulating
action of the battery charger in conjunction with the filtering action of the battery and the
inverter.
LEAD-ACID BATTERIES 23.87
Upon AC line power failure, the battery charger ceases to operate and the battery instantly
supplies power to the inverter and sustains the AC load without interruption. The synchro-
nizing signal is also lost during the power failure. The inverter, therefore, continues to operate
on its own internal frequency reference (
1% for standard units). The Ampere-hour capacity
of the battery determines the operating time of the system. The inverter is designed to
maintain a constant voltage output as the battery voltage drops during the discharge. When
AC power returns, the charger restores the battery energy and at the same time supplies
power to the inverter. A more detailed description of other types of UPS systems employing
VRLA Lead Acid Batteries is found in Sec. 24.8.
23.9.7 Marine Batteries
The marine battery market includes small and large leisure craft used for fishing, sailing,
and travel as well as larger commercial vessels engaged in towing, passenger transportation,
and workboat activities. In general lead-acid battery systems are used with system voltages
ranging from 6 to 220 V where recharging is accomplished by an engine generator or alter-
nator. Three types of designs are common: conventional flooded cells (mainly in the larger
cell designs), absorbed electrolyte designs, and gelled electrolyte designs. (The latter two
are VRLA batteries and are discussed in Chapter 24.)
Marine service differs from automotive in several aspects. Lights, refrigeration, blowers,
motors, radio, and other electrical equipment results in cycling service, with often a delay
between discharge and charge. In marine service, the batteries should have much greater
capacity than would normally be specified for the same horsepower equipment in a shore-
based application.
The key engineering features utilized by one prominent manufacturer of marine batteries
37
include the following:
•
A special grid design with heavier vertical and horizontal members.
•
High density active materials, both positive and negative.
•
Positive plates double insulated with thick woven glass matting and then sealed in a mi-
croporous polyethylene envelope.
In some designs, individual cells can be replaced while outer plastic cases provide high
impact and environmental protection.
REFERENCES
1. H. Bode, Lead-Acid Batteries, Wiley, New York, 1977.
2. H. E. Haring and U. B. Thomas, Trans. Electrochem. Soc. 68:293 (1935).
3. A. J. Salkind, D. T. Ferrell, and A. J. Hedges, ‘‘Secondary Batteries: 1952–1977,’’ J. Electrochem.
Soc. 125:311C (1978).
4. Battery Council International Annual Report.
5. P. Ruetschi, ‘‘Review of the Lead-Acid Battery Science and Technology,’’ J. Power Sources 2:3
(1977/ 1978).
6. C. Mantell, Batteries and Energy Systems, 2d ed., McGraw-Hill, New York, 1983.
7. D. J. G. Ives and G. J. Janz, Reference Electrodes, Academic, New York, 1961.
8. E. A. Willihnganz, U.S. Patent 3,657,639.
9. A. Sabatino, Maintenance-free Batteries, Heavy Duty Equipment Maintenance, Irving-Cloud Pub-
lishing, Lincolnwood, Ill., 1976.
23.88 CHAPTER TWENTY-THREE
10. Special Issue on Lead-Acid Batteries, J. Power Sources 2(1) (1977 /1978).
11. ASTM Specification B29, ‘‘Pig Lead Specifications,’’ American Society for Testing and Materials,
Philadelphia, Pa., 1959.
12. A. G. Cannone, D. O. Feder, and R. V. Biagetti, Bell Sys. Tech. J. 19:1279 (1970).
13. A. T. Balcerzak, Alloys for the 1980’s, St. Joe Lead Co., Clayton, Mo., 1980.
14. Grid Metal Manual, Independent Battery Manufacturers Association (IBMA), Largo, Fla., 1973.
15. N. E. Hehner, Storage Battery Manufacturing Manual, Independent Battery Manufacturers Associ-
ation (IBMA), Largo, Fla., 1976.
16. U. B. Thomas, F. T. Foster, and H. E. Haring, Trans. Electrochem. Soc. 92:313 (1947).
17. N. E. Hehner and E. Ritchie, Lead Oxides, Independent Battery Manufacturers Association (IBMA),
Largo, Fla.
18. G. W. Vinal, Storage Batteries, 4th ed., Wiley, New York, 1955.
19. M. Barak, Electrochemical Power Sources, Peter Peregrinus, Stevanage, U.K., 1980.
20. Battery Service Manual, 9th ed., Battery Council International, Chicago, 1982.
21. Battery Council International, 401 N. Michigan Ave., Chicago, Ill. 60611.
22. Battery Council International, Battery Replacement Data Book, 2000.
23. Gould Battery Handbook, Gould Inc., Mendota Heights, Minn., 1973.
24. E. J. Friedman et al., Electrotechnology, vol. 3: Stationary Lead-Acid Batteries. Ann Arbor Science
Publishers, Ann Arbor, Mich., 1980.
25. Bell Sys. Tech. J. 49(7) (Sept. 1970).
26. R. V. Biagetti and H. J. Luer, ‘‘A Cylindrical, Pure Lead, Lead-Acid Cell for Float Service,’’ J.
Power Sources 4 (1979).
27. A. G. Cannone, U.S. Patent 3,556,853, Jan. 19, 1971.
28. R. V. Biagetti, ‘‘The AT&T Lineage 2000 Round Cell Revisited: Lessons Learned; Significant Design
Changes; Actual Field Performance v. Expectations,’’ INTELECT—Int. Telecommunications Energy
Conf., Kyoto, Japan, Nov. 5–8, 1991.
29. E. Ritchie, International Lead-Zinc Research Organization Project LE-82-84, Final Rep., New York,
Dec. 1971.
30. ‘‘Handbook of Secondary Storage Batteries and Charge Regulators in Photovoltaic Systems.’’ Exide
Management and Technology Co., Rep. 1-7135, Sandia National Laboratories, Albuquerque, N.M.,
Aug. 1981.
31. G. E. Mayer, ‘‘Critical Review of Battery Cycle Life Testing Methods,’’ Proc. 5th Int. Electric Vehicle
Symp., Philadelphia, Pa., Oct. 1978.
32. C. J. Murray, Electrical Engineering Times, Issue 1128, Aug. 20, 2000.
33. Batteries International, Issue 42, pp. 71–76, Jan. 2000.
34. D. M. MacArthur, G. E. Blomgren, and R. A. Powers, 1999 Battery Industry Developments, Powers
Associates, Westlake, OH. (2000).
35. A. G. Cannone, U.S. Patent 4,605,605, Aug. 12, 1986.
36. A. G. Cannone, U.S. Patent 4,980,252, Dec. 25, 1980.
37. Product Literature, Rolls Battery Engineering, Salem, MA, 01970, USA.
24.1
CHAPTER 24
VALVE REGULATED LEAD-ACID
BATTERIES
Alvin J. Salkind, Ronald O. Hammel, Anthony G. Cannone, and
Forrest A. Trumbore
24.1 GENERAL CHARACTERISTICS
Lead-acid battery designs for many small portable, and some larger fixed applications, have
often been referred to as sealed and/ or maintenance free. This has been an accurate descrip-
tion to the extent that there was no need or opportunity to replace electrolyte. However,
virtually no design included a true hermetic seal, and only a pressure release valve which
limited inflow or outflow of gas to the cell. The valves released internal gasses at pressures
ranging from a few tenths of an atmosphere to a few atmospheres. In addition, most lead-
acid battery cases are molded of plastics, which are hydrogen permeable.
The newer designation for these designs is as a ‘‘Valve Regulated Lead-Acid Battery’’ or
VRLA. They differ from the conventional flooded lead-acid battery designs by containing
only a limited amount of electrolyte (‘‘starved’’ electrolyte) absorbed in a separator or im-
mobilized in a gel. In most designs, the cell capacity is limited by the amount of positive
active material. The starved electrolyte and excess of negative active material facilitate the
recombination of oxygen produced during overcharge or ‘‘float’’ charge with the negative
active material. The resealable valves are normally closed to prevent the entrance of oxygen
from the outside air. The vent pressure design depends on the manufacturer and predomi-
nantly by the case shape and material. VRLA designs have two usual shapes, one with
spirally-wound electrodes (jelly-roll construction) in a cylindrical container, and the second
with flat plates in a prismatic container. The cylindrical containers can maintain higher
internal pressures without deformation and can be designed to have a higher release pressure
than the prismatic cells. In some designs, an outer metal container is used to prevent defor-
mation of the plastic cases at higher temperatures and internal cell pressures. The range of
venting pressures includes a high of 25 to 40 psi for a metal-sheathed, spirally wound cell
to 1 to 2 psi for a large prismatic battery.
The electrolyte is commonly immobilized in two ways:
•
Absorbed electrolyte: A highly porous and absorbent mat, fabricated from microglass fi-
bers, is partially filled with electrolyte, and acts as the separator /electrolyte reservoir.
•
Gelled electrolyte: Fumed silica is added to the electrolyte, causing it to harden into a gel.
On subsequent charges, some water is lost, drying the gel until a network of cracks and
fissure develops between the positive and negative electrodes. The openings created provide
the path for the oxygen recombination reaction.
24.2 CHAPTER TWENTY-FOUR
It should be noted that silica reacts with sulfuric acid and the absorption or gelation is
chemical as well as physical in nature. The immobilization of the electrolyte allows batteries
to operate in different orientations without spillage. In larger industrial applications, the
batteries can be installed on their sides, permitting compact installations that use up to 40%
less floor space and volume. An orientation in which the plates are horizontal to the ground
is referred to as ‘‘pancake style.’’
1
Significant improvements in cycle life have been reported,
in some circumstances, in cells cycled with their electrodes parallel to the ground.
2
The use of VRLA designs is becoming more popular and accounted for over 75% of
telecommunication and UPS applications in 1999. The development of advanced charging
techniques has also increased the use of VRLA batteries in cycling applications such as
forklift service. New market opportunities in portable electronics, power tools, and hybrid
electric vehicles have stimulated the development of new designs of lead-acid batteries.
However, the VRLA designs do not have the capability of handling certain types of abuse
as well as conventional flooded batteries. The electrolyte, which provides the major internal
heat sink in cells, is much more limited in VRLA cells. As a result, VRLA designs are more
prone to thermal runaway under abusive conditions that pose little hazard for flooded cells.
This is particularly true when VRLA batteries are subjected to operations at elevated tem-
peratures. Recent discussion of high temperature (over 40
⬚C) effects as well as a discussion
of advantages and disadvantages have been given.
3,4
A detailed review of VRLA applications
has been given in a series of articles.
5
To insure long battery life under conditions of higher
temperature operations or overheating due to oxygen recombination, precautions must be
taken.
A comparison of gel designs with absorbed electrolyte designs in fork lift truck appli-
cations was presented
6
for one particular set of applications. However, new materials and
designs are evolving and the comparisons should be ongoing. Much activity is being reported
in the area of special fibers, blends, and surface treatments for the absorbing mat separators.
The major advantages and disadvantages of VRLA batteries are listed in Table 24.1.
TABLE 24.1 Major Advantages and Disadvantages of VRLA Batteries
Advantages Disadvantages
Maintenance-free Should not be stored in discharged condition
Moderate life on float service Relatively low energy density
High-rate capability Lower cycle life than sealed nickel-cadmium battery
High charge efficiency
No ‘‘memory’’ effect (compared to nickel-cadmium
battery)
Thermal runaway can occur with incorrect charging or
improper thermal management
‘‘State of charge’’ can usually be determined by
measuring voltage
Relatively low cost
Available from small single-cell units (2 V) to large 48 V
batteries
More sensitive to higher temperature environment than
conventional lead-acid batteries
VALVE REGULATED LEAD-ACID BATTERIES 24.3
24.2 CHEMISTRY
Although the design and the construction of the VRLA battery are different, its chemistry
is that of the traditional lead-acid battery. The basic ‘‘double sulfate’’ reaction applies to the
overall reaction:
discharge
——
PbO ⫹ Pb ⫹ 2H SO 2PbSO ⫹ 2H O
——
224
42
charge
The reaction at the positive electrode is
discharge
⫹⫺
——
PbO ⫹ 3H ⫹ HSO ⫹ 2e 2H O ⫹ PbSO
——
24
24
charge
and at the negative electrode,
discharge
⫺⫹
——
Pb ⫹ HSO PbSO ⫹ H ⫹ 2e
——
4
4
charge
When the cell is recharged, finely divided particles of PbSO
4
are electrochemically con-
verted to sponge lead at the negative electrode and PbO
2
at the positive electrode. As the
cell approaches complete recharge, when the majority of the PbSO
4
has been converted to
Pb and PbO
2
, the overcharge reactions begin. For conventional flooded lead-acid batteries,
the result of these reactions is the production of hydrogen and oxygen gas and subsequent
loss of water.
A unique aspect of the VRLA design is that the majority of the oxygen generated within
the cells at normal overcharge rates is recombined within the cell. The pure lead-tin grids
used in the construction minimize the evolution of hydrogen on overcharge. Most of the
hydrogen generated within the cell is released to the atmosphere through the vent or through
the plastic container.
Oxygen will react with lead at the negative plate in the presence of H
2
SO
4
as quickly it
can diffuse to the lead surface,
discharge
⫺⫹
1
——
Pb ⫹ HSO ⫹ H ⫹ ⁄
2
O PbSO ⫹ HO
——
42
42
charge
In a flooded lead-acid battery this diffusion of gases is a slow process, and virtually all the
H
2
and O
2
escape from the cell rather than recombine. In the VRLA battery the closely
spaced plates are separated by a glass mat which is composed of fine glass strands in a
porous structure. The cell is filled with only enough electrolyte to coat the surfaces of the
plates and the individual glass strands in the separator, thus creating the starved-electrolyte
condition. This condition allows for the homogeneous gas transfer between the plates, nec-
essary to promote the recombination reactions. Additional discussion of VRLA chemical
kinetics can be found in the literature.
4
The pressure release valve maintains an internal pressure and this condition aids recom-
bination by retaining the gases long enough within the cell for diffusion to take place. The
net result is that water, rather than being released from the cell, is cycled electrochemically
to take up the excess overcharge current beyond that used for conversion of active material.
Thus the cell can be overcharged sufficiently to convert virtually all the active material
without loss of water, particularly at the recommended recharge rates. At continuous high
overcharge rates (such as C /3 and above), gas buildup becomes so rapid that the recombi-
nation process is not as highly efficient, and O
2
as well as H
2
gas is released from the cell
as the cell vents. Charging at these higher rates should therefore be avoided.
24.4 CHAPTER TWENTY-FOUR
24.3 CELL CONSTRUCTION
24.3.1 VRLA Cylindrical Cells
7
A cross section of a VRLA cell and a breakdown of the basic components contained in the
cell are shown in Figs. 24.1 and 24.2. Both the positive and the negative grids are made
from 99.99% pure lead with 0.6% tin added for deep discharge recovery. The lead grid is
relatively thin, 0.6 to 0.9 mm, to provide for a high plate surface area and resultant high
discharge rates. The plates are pasted with lead oxides, separated by an absorbing glass mat,
and spirally wound to form the basic cell element. Lead posts are then welded to the exposed
positive- and negative-plate tabs. The terminals are inserted through the polypropylene inner
top and are effectively sealed by expansion into the lead posts. The element is then stuffed
into the liner and the top and liner are bonded together. At this state of construction, the
cell is sealed except for the open vent hole. Sulfuric acid is then added and the relief valve
is placed over the vent hole. The sealed element is then inserted into the metal can, the outer
plastic top added, and crimping completes the assembly. The metal case provides mechanical
strength and does not affect the operation of the resealable vent. The cell is then formed
electrochemically.
Monobloc batteries, using the cylindrical cell, are produced with two to six cells inter-
connected in a single plastic container. These 4-, 6-, and 12-V batteries have performance
characteristics similar to those of the single cell. The monobloc design is illustrated in Fig.
24.3. A newer type of small cylindrical lead-acid cell made within film electrodes has been
introduced.
8
This design has been characterized by Atwater et al.
9
for use in portable elec-
tronic and communication applications.
FIGURE 24.1 Cross section of the VRLA cell.
Components identified in Fig. 24.2. (Courtesy of
Hawker Energy Products, Inc.)
VALVE REGULATED LEAD-ACID BATTERIES 24.5
FIGURE 24.2 Components of VRLA cell. (Courtesy of Hawker Energy Products, Inc.)
FIGURE 24.3 Monobloc battery. (Courtesy of Hawker Energy Products, Inc.)
24.6 CHAPTER TWENTY-FOUR
FIGURE 24.4 Typical prismatic lead-acid cell and monobloc battery (a) Cut-
away view (Courtesy of Eagle-Picher Industries, Inc.)(b) Exploded view.
(Courtesy of Johnson Controls, Inc.)
24.3.2 VRLA Prismatic Cells
A cutaway view of a prismatic lead-acid cell is shown in Fig. 24.4a An exploded view of
a three-cell monobloc battery, using this prismatic cell, is given in Fig. 24.4b.
Nonantimonial calcium-lead alloys are usually used for the grids for the prismatic cell
because these grids have a lower self-discharge rate and reduced gassing. However, the
VALVE REGULATED LEAD-ACID BATTERIES 24.7
nonantimonial lead grids tend to reduce the deep-cyclability of the batteries unless additives
are incorporated into the cell. Most of these are proprietary, the most common being phos-
phoric acid. The balance between cyclability, capacity, and float life is controlled by the
ratio of
␣
-PbO
2
to

-PbO
2
, the paste density, the amount and concentration of the electrolyte,
the composition of the grid alloy, and the type and amount of additive.
The electrolyte is absorbed in blotterlike glass-fiber separators or is gelled. Many acid-
resistant materials, such as burnt clay, pumice, sand, Fuller’s earth, plaster of paris, and
asbestos, has been used for gelling. Present practice is to use fumed silica. When gelling
agents are used, the electrodes are usually formed with dilute acid for the first step of a
two-step formation, often in tanks. The gellation process is introduced in the final battery
assembly.
24.3.3 Thin Prismatic Cells
Thin flat prismatic sealed lead-acid cells have been designed for portable applications as
they offer more flexibility in the design of the battery. They use space more efficiently than
cylindrical cells, resulting in a higher volumetric energy density, and the slim design is
adaptable to small-footprint equipment.
10,11
An exploded view of a typical flat cell is shown
in Fig. 24.5.
FIGURE 24.5 Exploded view of typical thin, flat sealed lead-acid cell. Metal plates, each
approximately 0.3 mm thick, are laminated with special resin films to negative and positive
electrode plates, both physically and electrically. They are then fused to a resin frame by a
pressurized thermal bonding process. (Courtesy of Panasonic Industrial Co.)