Posts

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.

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.