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TTBLS structure grown with additives

Improving Deep-Cycle Batteries Through Additives

Battery manufacturers have improved deep cycle battery performance through the use of additives, but not all of them result in the same benefit to customers. At the core of all deep-cycle flooded lead-acid (FLA) battery technology is a basic design that has undergone continuous improvement over more than 100 years. Lead battery chemistry is one of the most reliable and cost-effective technologies over any other type of battery used in a variety of global industries. While these batteries have historically been the most widely used and the most recycled, a variety of additives and technologies have been introduced over the last few years to improve their efficiency to an even greater extent.

Grid Alloys

Historically, the primary failure mode of deep-cycle lead-acid batteries has been positive grid corrosion. The grid alloys used to manufacture deep-cycle flooded lead-acid battery plates typically consist of lead with additions of antimony to harden the soft lead, and to improve the deep cycle characteristics of the battery. Additional metals are often added to the lead-antimony alloys to improve strength and electrical conductivity. Another additive that is used to enhance lead-antimony alloys is selenium. Selenium acts as a grain refiner in lead-antimony alloys. This fine-grain alloy provides additional strength and corrosion resistance over conventional lead-antimony alloys. The effect of these improvements is that positive grid corrosion is no longer the primary failure mode, and the cycle life of FLA deep cycle batteries has been significantly increased.

Active Materials

The starting materials for deep cycle FLA positive active materials are made from a mixture of lead oxide, sulfuric acid, and various additives. These materials improve the performance and life of the positive electrodes in a finished battery. Historically, positive electrodes have been processed using a procedure called hydroset. This procedure is designed to ‘grow’ tetrabasic lead sulfate (TTBLS) crystals in the plates to provide the strength to resist the constant expansion and contraction of the active materials during cycling. This crystal growing process has limitations in its ability to control the range of sizes of the TTBLS crystals. Through the use of crystal seeding additives, the range of crystal sizes can be controlled to the most desirable sizes. These uniform crystal sizes in the TTBLS structure result in increased initial capacity, faster cycle-up to rated capacity, higher peak capacity, and improved charging using the wide range of charger technologies used in various applications.

Concurrent with the improvements in deep cycle FLA positive active materials, improvements in the performance of deep-cycle FLA negative active materials are needed. Carbon additives have been used in the negative active materials of lead-acid batteries for many years. These additives have been used in lead-acid battery expanders to prevent the natural tendency of the negative active material to shrink or coalesce during cycling. Negative active material shrinkage can reduce the capacity and life of deep-cycle FLA batteries. Recent improvements in these carbon materials have opened up new opportunities to improve several performance limitations of lead-acid batteries. New structured carbon materials such as graphites, graphenes, and nanocarbons have been used to control sulfation and improve chargeability in a partial state of charge (PSOC) applications such as renewable energy.

Although the basic structure of an FLA battery hasn’t changed for more than 100-years, manufacturers are continually searching for ways to improve efficiency while maintaining their cost-effectiveness. Additives are one of the ways FLA batteries are becoming more efficient, and new technologies to further enhance them are on the horizon.

AGM and Flooded Deep-Cycle Batteries

Understanding the Differences Between AGM And Flooded Deep-Cycle Batteries

When it comes to powering electric vehicles like golf carts, deep-cycle lead-acid batteries are the industry standard. The reason is that they are designed to provide the most cost-effective energy storage and delivery over the life of the battery.

Over the years, there have been two main types of deep-cycle lead-acid batteries that many golf car owners and fleets have used, the Flooded Lead-Acid (FLA) battery and the Absorbed Glass Mat (AGM) battery. While both provide optimum performance in a wide variety of applications, their design difference can offer various advantages depending on the application.

Engineering

The main design difference between FLA and AGM batteries is how the electrolyte is managed. In FLA batteries, the battery plates are submerged in the liquid electrolyte. During use, water in the electrolyte is broken down into oxygen and hydrogen gases and water is lost. This requires regular additions of water to be replaced to keep the battery plates fully submerged in the electrolyte.

In AGM batteries, the electrolyte is absorbed in special glass mat separators that retain all the electrolyte needed for the life of the battery.  Since there is no free electrolyte, the oxygen generated on a charge is recombined at the negative plate.  In normal operation, hydrogen is not generated and no water is lost.  This eliminates the need to add water and also allows the battery to be sealed with a one-way valve that prevents leakage of the electrolyte.

Performance Differences

FLA batteries have been used in a wide variety of applications for well over 150 years. Their popularity comes from their safety, reliability, and cost-effectiveness when compared with other types of rechargeable batteries.   According to Fred Wehmeyer, U.S. Battery Senior VP of Engineering, FLA batteries deliver the lowest cost per watt-hour both in acquisition cost and in overall cost per charge/discharge cycle.  “This is why they are the best choice for fleets of vehicles or equipment that are used heavily on a daily basis,” says Wehmeyer. “Also, both FLA and AGM batteries offer an environmental advantage over other types of batteries because they are essentially 100 percent recyclable and enjoy the highest recycling rate of any commercial product.”

AGM batteries offer the advantage of being maintenance-free. This can be significant in applications where regular maintenance is difficult or costly, such as when the batteries are located in remote or hard to access locations. Even though AGM batteries cost more per watt-hour, the elimination of maintenance costs reduces the overall battery operational costs.  Also, since the battery is sealed and does not emit gases in normal use, it can be used in sensitive areas such as food or pharmaceutical storage facilities.

Selecting between FLA or AGM deep cycle batteries ultimately depends on the type of use and the capability to provide regular maintenance in the application.

AGM = No Maintenance + Higher Cost + Susceptible to abuse like overcharging

FLA = Requires Watering + Lower Cost + Susceptible to abuse from poor maintenance

No matter what type of battery you use, it is always best to target the depth of discharge to 50 percent or less for both FLA or AGM battery types. This will optimize battery life cycle cost vs acquisition cost over the life of the battery system.

 

Testing Battery Specific Gravity with Hydrometer

Temperature’s Impact on Charging Deep-Cycle Batteries

The chemistry of flooded lead-acid deep-cycle batteries makes them one of the most cost-effective methods of energy storage. The composition of the battery’s design, however, makes it sensitive to temperature, which can affect its charging and discharging rate, something that should be addressed in regular maintenance routines.

Cold temperatures slow the rate of charging and discharge, while warmer temperatures increase the rates. This means that it may take longer for your batteries to fully charge in the winter than they will in the summer. Additionally, in the warmer summer months, batteries may discharge more quickly. Battery manufacturers use 80-degrees F (27 C) as the baseline temperature for optimum operation and calculating charge and discharge rates. Obviously that doesn’t work for everyone, so it’s important to take specific gravity readings with a hydrometer to know if and when your batteries are properly charged in all temperature conditions.

Specific gravity is the ratio of the weight of a solution to the weight of an equal volume of water at a specified temperature. A hydrometer can give you an indication of the state of charge of the battery’s electrolyte. A higher number indicates a higher concentration of acid in the electrolyte, indicating the battery is charged. A lower number indicates that the concentration of acid in the battery is less, showing the amount of discharge of the battery.

Battery manufacturers recommend using a simple correction factor to your hydrometer’s readings. Using 80-degrees as your baseline, subtract (.004) from your hydrometer reading for every 10-degrees below 80 °F (5.6-degrees below 27 °C). For example, if the temperature of the electrolyte is 50 °F and your battery specific gravity reading is 1.200, you must subtract .012 from your reading. In this case .004 for every 10-degrees equals .012. Subtract this from 1.200 and your corrected specific gravity reading is 1.188.

Specific gravity readings must be done on every cell of each battery in the pack. Compare the readings to the battery manufacturer’s specifications to indicate the state of charge of your batteries. While it’s not necessary to calculate your hydrometer’s readings for slight variations above or below 80 °F, it should be done in extreme weather conditions or seasonally to ensure that your battery-powered vehicles or equipment are performing at their best.

Connected 8v Batteries

Deep-Cycle Battery Terminals And Cable Maintenance Tips

When battery-powered vehicles and equipment suffer from intermittent performance issues, one of the most common reasons for this is poor battery cable connections. Ironically, loose connections can be caused by both under-tightening and over-tightening of the battery terminal connectors, as well as corrosion that can occur over time. Deep-cycle battery terminals are made from lead, which is a soft metal that creeps over time. The result is that they must be retightened regularly to maintain proper torque levels. If too much torque is applied when attaching cables to battery terminals, however, it can cause damage to the lead terminals preventing them from making a proper connection.  Battery manufacturers recommend terminal torque specifications that vary with the different types of terminals used for deep-cycle batteries.

Deep cycle batteries can come with UTL, UT, large and small L, Offset S, and SAE tapered post terminals, among others.  For UTL and UT battery terminals with threaded studs, the recommended torque is 95 – 105 in-lb (7.9 – 8.8 ft-lb).  For bolt-thru terminals such as large and small L and Offset S, the recommended torque is 100-120 in-lb (8.3 – 10 ft-lb).  SAE terminals have a recommended terminal torque of 50-70 in-lb (4.2 to 5.8 ft-lb). For other terminal types, consult the battery manufacturer’s recommendations. When measuring terminal torque, use a torque wrench with settings or readings in the 0 – 200 in-lb (0 – 16 ft-lb) range. Larger torque wrenches can inadvertently exceed the recommended settings or readings.

It is also important to consult the battery manufacturer’s recommendations for the proper type and assembly of the terminal hardware. Most manufacturers provide stainless steel nuts and lock washers or plated bolts, nuts, and lock washers with the batteries depending on the type of terminal used. The correct method is to position a lock washer between the nut and the connector (never between the connector and the lead terminal) and apply the recommended torque to completely compress the lock washer without deforming the lead terminal.

Clean terminals will maintain the best connection, so if corrosion is observed on the battery terminals and connectors, they should be cleaned with a wire brush and a solution of baking soda and water to neutralize any electrolyte that may be on the surfaces. To reduce the formation of corrosion on the terminals, battery manufacturers recommend using a corrosion inhibitor after making proper connections. Never apply grease or other lubricants between the terminals and connectors since they can interfere with the connection.

Check the cables to determine if they are corroded and need to be replaced.  Corrosion can extend under the cable insulation but is often not visible. A good ‘tug’ on the cables can expose weak connections. If new cables or connectors were added during the life of the vehicle, make sure the wire connectors are properly crimped and soldered to the cable ends.  Studies have shown that wire cables with crimped connectors that are not soldered to the cable ends can corrode faster and create a high resistance connection between the wire cable and crimped connector. This high resistance can cause excessive heating during discharge and melt the lead terminal, causing a loss of connection and permanent damage to the battery.  If any of the cables show signs of melted insulation, corrosion under the insulation, or have bare wire showing replace the cables and connectors.

While faulty connections are often the cause of battery terminal meltdowns resulting in poor performance, using appropriately sized wires with properly crimped and soldered connectors and the proper torque settings will reduce the chances that poor connections will adversely affect battery performance.

U.S. 145 XC2 with XC2 logo

Initial Capacity vs Rated and Peak Capacity for Deep-Cycle Batteries

Deep cycle batteries are designed to provide continuous power over an extended period of time and are then recharged in preparation for the next discharge/recharge cycle.  For many industrial and consumer applications where energy storage is critical, flooded lead-acid batteries provide premium performance at an unrivaled cost.  Consumers, however, may not be aware that flooded lead-acid deep cycle batteries are designed to reach their rated and/or peak capacity after a conditioning period of capacity ‘cycle-up’.  This cycle-up period consists of a series of discharge/recharge cycles in normal operation during which the available battery capacity increases with each cycle.  This conditioning cycle-up period is designed to provide the optimum in cycle life vs. cost for this type of battery and application.  The number of cycles required to achieve rated and/or peak capacity depends on many factors, including but not limited to battery design, recharge method, depth of discharge, temperature, etc.

Most deep cycle battery manufacturers provide a ‘Capacity Development Curve’ that describes the relationship of initial capacity and the number of cycles required to achieve rated and/or peak capacity for this type of battery.  The test procedures used to determine battery capacity ratings and capacity development relationships are specified in Battery Council International procedure BCIS-05 BCI Specifications for Electric Vehicle Batteries (Rev. 2010-15).  Per BCIS-05: “Long-life deep cycle EV batteries typically exhibit 75-80% of rated capacity on initial discharge, full rated capacity within the first 100 cycles, and >100% of rating at peak capacity.”

To achieve optimum cycle life vs. battery acquisition cost, most battery manufacturers recommend sizing the battery’s capacity to ~50% depth of discharge (DOD).  This not only optimizes the cycle life of the battery vs. cost but also provides a ‘reserve’ capacity in situations where additional runtime is needed beyond normal requirements.  Since flooded lead-acid deep cycle batteries can continue to deliver useable capacity down to ~50% of rated capacity, this recommendation also allows utilization of the total number of cycles available from the battery.  For these reasons, the fact that this type of battery does not deliver full rated capacity ‘out-of-box’ is not usually an issue and can easily be managed through proper battery sizing and choice of battery type and manufacturer.

Battery manufacturers do recognize that fleets operating battery-powered machinery such as aerial platform lifts, floor cleaning machines, pallet jacks, and golf carts desire the highest possible capacity over the life of the battery.  Accordingly, they are constantly improving battery designs and charging methods to achieve the highest possible initial capacity and the fastest possible cycle-up without compromising overall cycle life.