Because of the growing number of performance rating schemes and/or ways to value your buying decision in the market today, it has become difficult to make a decision that doesn’t come with some form of buyer’s remorse at a later date. The following are some of the more obvious things to watch out for when buying:

• Some companies rate their Reserve Capacities (minutes that the battery will deliver a discharge current) at 23 amps instead of the industry standard (BCI published) way of establishing Reserve Capacity at 25 amps.
• Amp Hour (AH) ratings can be at 5-hour, 10-hour, 20-hour and even 100-hour rates, so make sure you compare the same rate.
• Cranking Amps (the ability of the battery to deliver a higher starting current over a shorter period for engine starting) are given at different temperatures, so make sure that you compare the published “Cranking Amps” of each battery at the same temperature. CCA or Cold Cranking Amps at 0°F/-18°C is the industry standard rating. You may see ratings published at CA, MCA, MCCA and HCA. All reputable suppliers will publish the CCA.

Some companies have invented their own rating system by recognizing that the process of comparing deep-cycle batteries should be simplified. An American-based manufacturer of batteries invented a new labelling system incorporating the “Lifetime Energy Unit” (LEU). This was their attempt to help a buyer determine the lifetime performance and value of any given battery in the market. Simply stated, and in the words of the SANTA FE SPRINGS, CA. Manufacturer,  “Lifetime Energy Units " signifies the kilowatt-hours of energy a battery delivers over its lifetime. The bigger the number, the total work the battery can perform. Before introducing LEUs, accurately determining battery performance and value required complex calculations. Engineers compute the true worth of a battery as the total energy it contains, measured in kilowatt-hours (KWH). To derive a number for KWH, they build a curve that profiles the relationship between runtime and the number of cycles. The area under the curve is the total energy the battery delivers over its lifetime. When amp-hours are multiplied by battery voltage, the result is the battery's capacity in watt-hours. The next step - comparing a battery's value - is also simplified. By dividing the LEU by the battery's price, the prospective purchaser obtains a value figure (energy units per dollar) that ensures an apples-to-apples comparison between competing products.”

Discover ultimately rejects this position. As with the variations in determining Reserve Capacity and Cranking Amps mentioned earlier, this is NOT a recognized Battery Council International (BCI) method for rating or comparing batteries as suggested by the manufacturer. The manufacturer leaves out the exact method of determining LEUs, for an exact comparison to be done, which was their stated purpose for establishing the rating. This creates a situation where two suppliers could use two sets of methodologies to determine their respective LEUs, making reasonable comparisons impossible. This implies that the LEU idea or concept is simply a marketing tool with no real scientific basis for engineers, as the manufacturer suggests.

LEUs – as a way of helping buyers make an informed decision – would work very well if the buyer was given some additional pieces of data (data that IS available from other manufacturers and that could be used to make meaningful comparisons):

1. The exact discharge control methods (test procedures) used in determining the battery's “Cycle Time” (what discharge rate and to what depth is the battery discharged?).
2. Whether or not the batteries can be pre-conditioned before running the procedure.
3. The resulting ampere hours of power discharged per cycle
4. The recharge control methods (test procedures) before the next discharge procedure.
5. The exact control methods used in determining the battery's “Life Cycles.”
6. The resulting ampere hours of power discharged over the life of the battery.

In addition to the problems listed above for making good performance comparisons amongst different batteries, using the LEU marketing tool to make a serious value comparison is equally flawed. The value comparison requires more detail. Some, but certainly not all, of the issues to be examined and required in determining value are:

1. Time and Supply costs associated with servicing the battery (as recommended by the manufacturer) to ensure it achieves its assumed life cycles.
2. Costs associated with Workers' Safety and Clothing needs (as recommended by the manufacturer).
3. The cost associated with Environmental Issues, Storage and Equipment Damage resulting from the emission of free hydrogen molecules during discharge and recharge.
4. Freight/time costs and/or restrictions related to shipping.

If these data were known, the buyer could then determine the true energy units per dollar or lifetime energy value as suggested by the manufacturer who introduced the LEU calculation.

What to consider when buying a deep-cycle battery

It is our opinion that to determine the actual best “bang for your buck” for batteries in cycling applications, you should gather the following information and perform the following calculations:

Information gathering before buying? Determine the amount of energy the battery will deliver in its life using test procedures recognized by worldwide manufacturers and published in the BCI technical manual. This information should be available from all manufacturers and should include the following:

• Discharge current used (25Amps, 75Amps, 20-hour rate, etc.)
• Discharge time (Cycle Life) to an effective 100% depth of discharge (1.75 volts per cell)
• Discharge cycles (Life Cycles) achieved before the battery could not deliver at least 50% of its original rated capacity

NOTE: Different types of batteries use test procedures that allow different end-of-life criteria. For example, an electric vehicle or standard deep-cycle product would be considered at its end of life when it could not deliver 50% of its rated capacity. At the same time, a golf cart battery would not be determined to be at its end of life until it could produce at least 1.75 volts per cell during 40 minutes of discharge at 75 amperes. 

Determine the number of times the battery will be serviced in its lifetime, as the manufacturer recommends. It is important to use the manufacturer's recommended service schedule. For time/cost analysis, we recommend you use an average of 10 minutes per service per battery. 

Determine the average per hour/minute labour costs in your organization. This number varies by region and industry - should not include anything but direct labour costs. You can safely use a figure of $18.00 - $25.00 per hour ($.30 - $.42 per minute) (2003 dollars) without benefits etc. One transit authority stated that their direct labour cost associated with maintaining batteries in each transit bus was $180.00 per year; another stated it was as high as $550 per battery. We suggest using $22.00 as an average hourly cost ($.367 per minute). 

Cost of service materials over the life of the battery, such as; distilled or specially treated water - using a per cell fluid usage by volume of 20% on an average cell volume of 2.35l/80oz and a 75% consumption efficiency or between $.02-$.04 per oz. Battery fluid volumes are as low as 5l/169oz and as high as 16l/540oz; cleaning and neutralizing agents at 1oz per battery or $.25 per battery per service; special clothing; repair and replacement of battery boxes and trays and more.

Cost Per Battery

• Purchase price of the battery
• Freight or handling charges (overland or can they be shipped through courier or air)

Calculating Cost to Own

Estimate the cost of materials used when servicing the battery as the manufacturer recommends. For comparison, it is reasonable to use just $1.70 each time for distilled water, cleaning and neutralizing agents and ignore the other variable costs. Multiply this amount by the years the manufacturer says the battery will last in the application. Multiply the result by the number of times the manufacturer says the battery should be serviced per year to achieve the published life expectancy. Our experience shows that most manufacturers will recommend your service flooded batteries at least once a month. 

Two of the “World's” leading manufacturers and sellers of Flooded, GEL and AGM Deep-cycle batteries state the following on their websites:  “Flooded batteries need water. More importantly, watering must be done at the right time and in the right amount or the battery’s performance and longevity suffers. Water should always be added after fully charging the battery. Before charging, there should be enough water to cover the plates.” This would suggest that the world’s leading manufacturers of flooded deep-cycle batteries recommend that service is required, particularly as the battery ages, BEFORE and AFTER every charge/discharge cycle. In some cases, they suggest that failing to do so will void the warranty. If you cycle the battery two times per week, the battery will last approximately three years following the manufacturer's recommended service procedures. This means your per battery service material costs will be at least $1.70 x 12 services per year x 3 years = $61.20. If you serve as the manufacturers suggest, it will be as much as $1.70 x 104 services per year x 3 years = $530.40. Our experience shows that for a battery to last three years when being cycled two times per week, it needs to be serviced at least once every four cycles or bi-monthly. $1.70 x 3 years x 26 services = $132.60 per battery. Every user of deep-cycle batteries is familiar with dried “rotten egg” smelling batteries, the result of NOT maintaining a proper service schedule over the battery's life.

NOTE: when asked, more than 80% of equipment managers could not produce or describe a “battery service schedule” - for equipment under their supervision that uses cycling batteries.

In our opinion, if you were to match a quality flooded battery against a Discover Semi Traction EV Dry Cell AGM or GEL battery of the same size and AH rating for use in the same application, you would find the total cost of ownership to be higher for the flooded battery option. Discover Semi Traction EV Dry Cell AGM or GEL batteries require less service, and as a result, with proper charging methods, Discover batteries will out-value flooded batteries. It is more likely that the standards of service for the flooded batteries will not be met in the real world. Therefore, it will not meet the manufacturer's required levels to achieve maximum life.

Additionally, when considering flooded versus Dry Cell AGM or GEL, one must also consider other inconveniences and/or costs associated with servicing, working with or having sensitive equipment around flooded batteries. These would include, but are not limited to:

• damaged and/or special clothing
• battery compartment repairs
• air quality problems
• workers compensation claims
• occupational health issues
• hazardous materials handling requirements
• shipping restrictions
• damage to service areas from acid and corrosive by-product spills

We feel the more competitive and demanding the channel (jobber/installer/large user/rental equipment), the more compelling and feasible the switch to Discover Semi Traction EV Dry Cell AGM or GEL batteries becomes. The larger the bank of batteries used, the more important costs associated with service and the more compelling and feasible the switch to Discover batteries becomes.

Discover has made available the largest range of AGM and GEL Semi-Traction (Industrial deep-cycle), deep-cycle (and high-cycle AGM, AGM SVR and GEL product lines worldwide! This means you have several sizes and performance options when making your purchase decision. First, consider the following:

• Do you have any size restrictions (Height, total W x L area available)
• Do you have multiple areas available for batteries? If so, how far apart are they, and are they similar in area?
• Is the area hard to get to, or will it be easy to install heavy batteries?
• Do you have weight restrictions? Both on a per-battery basis and as a total installation.
• Will the installed batteries be easy to service? If not, DO NOT consider Flooded types!
• Does a dedicated exhaust fan service the installation area? If not, DO NOT consider Flooded types!
• What type of battery(s) are you using now?
• What type of charging system do you have?

With these questions answered, you are now ready to consider your options. Make sure you have read and understand the sections on How do I increase the capacity of my battery and system?

What should I look for when buying deep-cycle batteries?

The essential consideration in buying a deep-cycle battery is first to make sure the battery you are considering is a “True or Real” deep-cycle battery. Once you have determined that the battery type is correct, make sure the Ampere-Hour or Reserve Capacity rating of the battery will meet or exceed your requirements. Most deep-cycle batteries are rated in discharge rates of 100 hours, 20 hours, 10 hours, 8 hours or 5 hours, and/or reserve capacity minutes.

Reserve Capacity (RC) is the number of minutes a fully charged lead-acid battery at 80° F (26.7°C) can be discharged at 25 amps before the voltage falls below 1.75 volts per cell (100% DOD). To convert RC to Ampere-Hours at the 25 amp rate, multiply RC by .4167.

It is better to have more ampere-hours (or RC) because, within the same battery type, footprint or industry group size, the battery with higher ampere-hours (or RC) will tend to deliver longer discharge times. It is also essential to know the electrochemical battery design. A 100 ampere-hour battery of a particular dimension designed for UPS applications may deliver more initial runtime than a Traction or Deep-cycle battery of the same dimension. Still, it will not provide the life or number of cycles that the Traction or Deep-cycle battery will. Contrary to popular belief, battery weight (while necessary) is “not” the perfect indication of the quality of one battery to another. It is almost certain that if two batteries of the same dimension are weighed - one battery designed for UPS service and the other battery designed for Deep-cycle service- the UPS battery should weigh more. Be sure you understand what you are buying!

The “Battery Council International” manual BCIS-05 Rev. Dec02 provides some guidance with amp hour capacity relationships when comparing battery design for the same service application. In it, they state that “for guidance in establishing rates, ampere-hour capacity relationships are approximate”:

• 20 hour 125%
• 3 hour 82%
• 6 hour 100%
• 2 hour 72%
• 5 hour 95%
• 1 hour 55%
• 4 hour 89%

Finally, the available space and weight restrictions will have to be considered when determining the appropriate deep-cycle battery.

If you are using a non-temperature compensated hydrometer, make the adjustments in the table below.

For example, at 30° F (-1.1° C), the specific gravity reading would be 1.245 for a 100% State-of-Charge. At 100° F (37.8° C), the specific gravity would be 1.273 for a 100% State-of-Charge. This is why a temperature-compensated hydrometer is highly recommended and more accurate than other means when testing flooded battery types.

For non-sealed batteries, check the specific gravity in each cell with a hydrometer and average the readings.

Table 2 - Hydrometer Temperature Compensation

How do I temperature compensate for my voltmeter readings?

If you are using a digital voltmeter, make the adjustments in the table below. For example, at 30° F (-1.1° C), the voltage reading would be 12.53 for a 100% State-of-Charge. At 100° F (37.8° C), the voltage would be 12.698 for 100% State-of-Charge. For sealed batteries, measure the Open Circuit Voltage across the battery terminals with an accurate digital voltmeter. This is the only way to determine the State-of-Charge on sealed, non-accessible batteries.

Table 3 - Voltmeter Temperature Compensation

High deep-cycle demands on battery-powered equipment and the increased cyclic demand and parasitic electrical loads brought about by the use of Start-Stop technologies, increased electrical systems in modern vehicles, and the frequent partial state of charge (PSOC) operation combine to accelerate the #1 cause of declining battery life expectancy: Acid Stratification. Acid stratification happens naturally in flooded lead-acid batteries. The fluid in a battery is called the electrolyte. The electrolyte is a mixture of sulfuric acid and water. Acid is heavier than water and is fundamental to a lead-acid battery's electrochemical charge and discharge process. Acid stratification happens when the heavier acid in the battery’s electrolyte separates from the water and assembles at the bottom of the battery’s cell, creating an area of very high specific gravity electrolyte.

What are the Effects of Acid Stratification?

• In wet flooded batteries, acid stratifies (sinks to the bottom of the battery’s cells). The upper portion of the battery’s plates is left subject to low specific gravity electrolyte (now mostly water). The upper portion of the plate is rendered inactive and can no longer support discharge capacity. Under these conditions, the useful active material in the battery will be reduced by as much as 40% within six months of normal use, creating “dead lead” or “inactive active material.” (See Figure 1)
• The stratified acid at the bottom of the battery’s cell focuses discharge activity to the bottom of the cell, causing the bottom part of the plate to work overtime. While the bottom part of the plate gets excessively discharged, the top part of the plate receives most of the charging activity. As a result, acid stratification can cause a battery’s dynamic charge acceptance1 (“DCA”) to decline by 50% to 70% within six months of installation, increasing alternator wear and tear and decreasing fuel efficiency.
• Since electrical current moves more easily through water (top part of the cell) than it does through acid (bottom part of the cell), stratified acid concentrates charging current and charging heat at the upper part of the plate, accelerating corrosion which dramatically lowers the battery’s cranking power (“CCA”)
• Stratified acid promotes increased internal resistance, lower conductivity and accelerated sulfation on the lower part of the plates, reducing the battery’s dynamic charge acceptance. This means a sulphated battery will only accept a surface charge, resulting in a false positive state of charge readings to vehicle computers and battery testers. So, a battery may appear fully charged but only provide low “CCA” and “AH”/”RC.”

Acid stratification is accelerated if:

1. The battery operates in a partial state of charge (PSOC)
2. The battery seldom receives a full charge
3. The battery is constantly micro-cycled between 3% - 17.5% DOD as in start-stop vehicles
4. The battery is regularly high cycled between 17.5% and 30%
5. The battery is regularly deep-cycled beyond 50% DOD
6. The battery is used or exposed to extreme temperatures, and
7. The battery is left standing for long periods

All of these conditions contribute to premature battery failure.