Frequently Asked Questions

Trojan Battery provides answers to commonly asked questions. 

Please review this list to see if there is an answer to your question.  In addition, please consult Trojan’s User Guides, or take a moment to view one of our Trojan Tips videos for additional information on battery maintenance.

bttn_MeasurementsTroubleshooting bttn_Maintenance bttn_Ratings bttn_Charging
bttn_DateCodes bttn_AdditivesExternalComponents bttn_BatterySelection bttn_CommonMistakes
bttn_TemperatureFactorsEffects bttn_BatteryRecycling bttn_BatteryMyths

Measurements & Troubleshooting

1. How can I tell if a flooded battery is bad?
To determine if the battery in a system is experiencing a problem, disconnect all electrical loads, fully charge the batteries then disconnect all charging sources. Allow each battery in the system to stand on open-circuit for about one hour. Measure the voltage of each battery. If the battery voltage spread exceeds .15 volts for a 6-volt battery, or .22 volts for a 12-volt battery a problem is indicated. Battery voltage alone does not confirm a problem. When the voltage spread indicates a problem, confirmation is accomplished by taking electrolyte specific gravity readings using a hydrometer. If the specific gravity readings show a spread greater than .030 (30 points), give the batteries an equalization charge and re-test.

2. How can a flooded battery’s state of charge be accurately measured?
The state of charge of a lead acid battery is most accurately determined by measuring the specific gravity of the electrolyte. This is done with a hydrometer. Battery voltage also indicates the level of charge when measured in an open circuit condition. This should be done with a voltmeter. For an accurate voltage reading, the battery should also be allowed to rest for a period of one hour minimum in order to let the voltage stabilize.

3. How far can I tilt my batteries?
For flooded batteries, 22 degrees from vertical is the maximum recommended tilt. AGM and Gel batteries can be operated vertically or horizontally.

4. Can I reduce my maintenance by not gassing my flooded batteries?
You will reduce the frequency of watering, but will cause a condition known as stratification where the specific gravity of the electrolyte is light at the top of the battery and heavy at the bottom. This condition results in poor performance and reduced battery life.

5. What is used to clean a battery and neutralize the electrolyte?
A solution of baking soda and water. Use 1 cup of baking soda for every gallon of water.

6. What is the specific gravity of a fully charged flooded battery?
A hydrometer reading of 1.277 or greater indicates full charge for most Trojan batteries. This value is based upon a specified temperature of 80°F (27°C). For temperature correction values, see the “Temperature” section of this FAQ.

7. What is the correct Specific Gravity (SG) of the Trojan Premium Line? I was told that Trojan changed the SG value for the Premium Line. Is this true? How do I determine the correct Specific Gravity of the Trojan Premium Line battery I already have purchased?
Yes, Trojan changed SG values of the Premium Line in March 2012 to avoid confusion over correct SG values for the Premium Line compared to the Signature Line. However, this change does not have any impact on life cycle performance. Trojan Premium Line batteries manufactured prior to March, 2012 have nominal SG of 1.260 while those produced after March 2012 have nominal SG of 1.280. To determine the date of manufacture, refer to the date code on the negative terminal which consists of a letter and a number. The letter refers to the month and the number refers to the year. A2 = January 2012, B2 = February 2012 and C2 = March 2012 etc.

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1. What is the shelf life of my battery?
The limiting factor of battery’s shelf life is the rate of self-discharge which itself is temperature dependent. VRLA batteries will self-discharge less than 3% per month at 77º F (25º C). Flooded batteries will self-discharge up to 15% per month at 77º F (25º C). VRLA batteries should not be stored for more than 6 months at 77º F (25º C) without recharged. The specific gravity or voltage of flooded batteries should be monitored every 4 – 6 weeks and should be given a boost charge when they are at 70% stat of charge (SOC). When batteries are taken out of long storage, it is recommended to recharge before use.

2. Can I use the specific gravities to troubleshoot my battery?
The specific gravities of batteries are an excellent tool to determine the state of charge of batteries and their ability to accept a charge. Unfortunately, the specific gravities can also lead to an erroneous conclusion if we do not specify the conditions under which the measurements were taken. The two major sources of error in measuring specific gravities are lack of temperature compensation and water addition. Since the specific gravities of batteries are affected by temperature, the measurements must be temperature compensated. The best way to compensate for cold temperatures is to subtract 4 points from your reading for every 10º F (5.5º C) degrees below 80º F (27º C). To compensate for hot temperatures simply add 4 points from your reading for every 10º F (5.5º C) degrees above 80º F (27º C). Also, the addition of water should only be done once the batteries are fully charged as the electrolyte levels vary as a function of state of charge and are highest once the batteries are fully charged. Please use distilled water only and note that adding water will lower the specific gravities of your batteries. The specific gravities cannot be used as a reliable source unless we account for the two sources of error mentioned above.

3. Is it normal for my flooded batteries to lose water?
It is completely normal for flooded batteries to lose water. They lose water because of the gassing that they go through with every charge. Gassing is an important part of the recharge process. The gassing allows the electrolyte to mix well and helps the battery get back to a fully charged state at the end of the charge process. Unfortunately, the gassing also causes water to be lost. The addition of water should be only be done once the batteries are fully charged as the electrolyte levels vary as a function of state of charge and are highest once the batteries are fully charged. The correct electrolyte level is about 1/8th of an inch below the bottom of the vent well. Please use distilled water only.

A. When adding water to the L16RE-2V battery, please ensure that you add water to all 3 caps.

4. When should I water my flooded batteries?
Water is lost during the charging of flooded batteries. The best time to water your batteries is always at the end of the charge cycle however, if the plates are exposed to air, add just enough water to cover the plates before starting the charge cycle. When the charging process is complete, re-check the electrolyte and top off as needed.

5. How often should I water my flooded batteries?
It is best to check your new batteries regularly as this will give you a good feel for how often your application will require battery watering. WARNING: A brand new battery may have a low electrolyte level. Charge the battery first and then add water if needed. Adding water to a battery before charging may result in overflow of the electrolyte.

6. Can I add de-ionized water to my flooded batteries instead of distilled water?
Yes, de-ionized water can be used instead of distilled water. However, distilled water is preferred because although de-ionized water has all free ions removed, it may still contain some minerals that may be harmful to the battery. In addition, distilled water is generally more available than de-ionized water.

7. What is the proper electrolyte level?
Liquid levels should be 1/8 inch below the bottom of the vent well (the plastic tube that extends into the battery). The electrolyte level should not drop below the top of the plates. See Battery Watering Diagram.

8. What is the proper torque value for my battery connections?

Terminal Type Terminal Type Torque (in/lbs) Torque (N•m)
ELPT, EHPT, EUT, LT, WNT, DWNT, UT 95 – 105 11 – 12
EAPT, AP 50 – 70 6 – 8
IND 100 – 120 11 – 14
M6 30 3 – 4
M8 85 – 95 10 – 11
ST 120 – 180 14 – 20

WARNING: Do not over tighten terminals. Doing so can result in post breakage, post meltdown, and fire.

9. Can a flooded battery freeze?
The only way that a battery can freeze is if it is left in a state of partial or complete discharge. As the state of charge in a battery decreases, the electrolyte becomes more like water and the freezing temperature increases. The freezing temperature of the electrolyte in a fully charged battery is -92º F (-69º C). At a 40% state of charge, electrolyte will freeze if the temperature reaches approximately 16º F (-9º C).

10. What is the life expectancy of my battery?
The life expectancy of batteries in very dynamic and depends on a number of application specific variables. The life expectancy depends on the proper sizing of the battery bank, depth of discharge, type of loads, battery maintenance regime, ambient temperature, and charging algorithm.

11. Can I do a partial replacement of my flooded batteries?
We do not recommend partial battery replacement of flooded battery banks. The behavior of batteries during discharging and charging varies throughout their lifespan and if all the batteries are the same age, than they all will have similar responses. The danger with replacing only one battery is that the older batteries tend to require more charge than newer batteries, and since the new batteries are in the same circuit, they too will be overcharged. There is also the chance that the older batteries will be undercharged since the overall voltage response of all the batteries (old and new) will not be a good representation of either group. The charging system might erroneously think that ALL the batteries have reached the desired voltage and it may stop the charging of the batteries prematurely.

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1. What are the 20-hour and 100-hour rates?
The 100-hour rate is just an index that is used in the battery industry to compare batteries of different types and sizes. The 100-hour rate is the amount of Ahs the battery will deliver during a 100-hour discharge. The capacity of a battery, in Ahs, is a dynamic number that is dependent on the discharge current. For example, a battery that is discharged at 10A will give you more capacity than a battery that is discharged at 100A. With the 100-hr rate, the battery is able to deliver more Ahs than with the 20-hr rate because the 100-hr rate uses a much lower discharge current than the 20-hr rate. Both rates are used as baselines in different parts of the world. Either rate, however, will give you the same view of a battery. A higher capacity battery will have higher 5 and 20 hour rates than a battery with lower capacity.

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1. When do I need to perform an equalization charge?
Equalizing should be performed when a battery is first purchased (called a freshening charge) and on a regular basis as needed. How often this might occur with your battery will vary depending on your application. You will need to monitor your battery voltage and specific gravity to determine when equalization is needed. For example, it is time to equalize if the measured specific gravity values are below manufacturer’s recommended values after charging (recommended value for Trojan Deep Cycle batteries is 1.285 +/- .007 at 80º F (27º C)). Equalizing is also required if the specific gravity value of any individual cell varies 30 points or more. In addition, reduced performance can also be an indicator that equalizing is necessary. Equalization should be performed when individual battery voltages in a battery pack range greater than 0.15 volts for 6-volt batteries or 0.30 volts for 12-volt batteries.

2. Does my deep cycle battery develop a memory?
Lead acid batteries do not develop any type of memory. This means that you do not have to deep discharge or completely discharge a battery before recharging it. For optimum life and performance, we generally recommend a discharge of 20 to 50% of the batteries rated capacity even though the battery is capable of being cycled to 80%.

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Date Codes

1. How do you read the date codes on the batteries?
Negative Terminal- Shipping Date. This code indicates the month and year when the battery was shipped out of our factory. LETTER stands for the month, A to L (A=January, B=February, C=March, and so on); NUMBER is the last digit of the year.


  • A battery with “G4” on the negative.
  • G4” means that it was shipped from our factory around July of 2014.
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Additives & External Components

1. Can I use battery additives?
Trojan Battery, along with other battery manufacturers, do not recommend that you add anything to your batteries other than distilled water. Extensive testing has shown that most of these additives do not work as advertised; in fact, some may do more harm than good. Be aware that adding anything other than water to your batteries will void the warranty.

2. Do you recommend the use of desulfators?
We don’t recommend the use of desulfators or any other external device, as they tend to do more harm than good. No external device or chemicals need to be added to our products – only distilled water.

3. Do you ever add acid to a battery?
Under normal operating conditions, you never need to add acid. Only distilled, deionized or approved water should be added to achieve the recommended levels mentioned above.

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Battery Selection

1. How do I select the right battery for my application?
Proper battery selection may require the assistance of a knowledgeable battery sales/service technician.

Please contact your local Trojan Battery dealer or call us at 1-800-423-6569 or 562-236-3000 and ask for assistance from one of our Applications Engineers.

2. What is the difference between a deep cycle battery, a starting battery, and a dual-purpose battery?
A deep cycle battery has the ability to be deeply discharged and charged many times during its service life. It is designed specifically for powering electrical equipment for long periods of time. An automotive or starting battery is designed for brief bursts of high current and cannot withstand more than a few deep discharges before failure. This is why it is unable to start your car if you accidentally leave the lights on more than a couple of times. For applications where both engine starting and light deep cycling are required, a dual-purpose battery is often used. This type of battery is neither a starting nor a deep cycle battery but rather a compromise between the two so it performs both functions adequately. Only deep cycle batteries should be used in renewable energy applications.

3. What’s better? 24 Volt or 48 Volt systems?
Systems with loads greater than 100 watts continuous will be better served by higher voltages such as 24 and 48 volts due to the reduced size of wiring required to minimize voltage drop which impacts overall system cost and ease of installation.

4. Why do manufacturers use different alloys in their batteries (lead-calcium, lead-antimony, lead selenium, etc.)?
The composition of the plate grid alloy can have a major effect on operating characteristics, such as behavior on float charging and cycle life. Older lead-antimony designs have good cycling capability but require frequent water additions, particularly towards the end of life, due to antimony migration between the plates. Cells with lead-calcium alloys require far less watering, but tend to have a poor cycle life. Lead-selenium alloys are actually low-antimony types with the addition of selenium as a hardening agent. Such alloys promote good cycling capability, while maintaining a constant and fairly low level of water consumption. Many variants on these alloy types are commercially available.

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Common Mistakes

1. What are common mistakes made by flooded battery owners?
Undercharging: Continually operating the battery in a partial state of charge, or storing the battery in a discharged state results in the formation of lead sulfate compounds on the plates. This condition is known as sulfation. Both of these conditions reduce the battery’s performance and may cause premature battery failure. Undercharging will also cause stratification.

  • Overcharging: Continuous charging causes accelerated corrosion of the positive plates, excessive water consumption, and in some cases, damaging temperatures within a lead acid battery.
  • Under watering: In flooded batteries water is lost during the charging process. If the electrolyte level drops below the tops of the plates, irreparable damage may occur. Water levels should be checked and maintained routinely.
  • Over-watering: Excessive watering of a battery results in additional dilution of the electrolyte, resulting in reduced battery performance. Additionally, watering the battery before charging may result in electrolyte overflow and unnecessary additional maintenance.
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Temperature Factors & Effects

1. How does temperature affect the performance of my batteries?
At higher temperatures (above 80º F (27º C)) battery capacity generally increases, usually at the cost of battery life. Higher temperatures also increase the self-discharge characteristic. Colder temperatures (below 80º F (27º C)) will lower battery capacity and prolong battery life. Cooler temperatures will slow self-discharge. Therefore, operating batteries at temperatures at or slightly below 80º F (27º C) will optimize both performance and life.

2. How do I determine my battery capacity when it is colder/hotter?
Battery capacity is basically a linear relationship. A good rule of thumb is that for every 15º F (9º C) above 80º F (27º C), capacity is increased by 10% and for every 15º F (9º C) below 80º F (27º C), capacity is reduced by 10%.

3. How do I account for temperature when taking my gravity readings?
Temperature will affect specific gravity readings. As temperature increases, the electrolyte solution expands and as temperature decreases the electrolyte solution contracts. As a result, it is a good practice to temperature correct specific gravity readings. Here are the relationships Trojan recommends using: Every ten degrees above 80º F (27º C) add 4 points to the hydrometer reading.

  • Example: @ 90º F (32º C) the hydrometer reads: 1.250 the actual reading: 1.250 + .003 = 1.253.
      For every ten degrees below 80º F (27º C) subtract 4 points from the hydrometer reading.

      • Example: @ 70º F (21º C) the hydrometer reads: 1.250 the actual reading: 1.250 – .003 = 1.247.

4. How much should I compensate the charge voltage for temperature?

            Temperature will affect voltage readings. As temperature increases, voltage decreases. Conversely, as temperature decreases, voltage increases. Here are the relationships:

            • Trojan recommends using the following: For every 1º F below 77º F add 0.0028 volts per cell or for every 1 C below 25º C add 0.005 volts per cell to the charger voltage setting.
              • 1: A 12 volt battery @ 70º F. The recommended charging voltage at 77º F is 14.8 volts. The adjusted charging voltage is 14.8 + (6 cells * 7 degrees below * 0.0028) = 14.92 volts.
              • 2: A 12 volt battery @ 21º C. The recommended charging voltage at 25º C is 14.8 volts. The adjusted charging voltage is 14.8 + (6 cells * 4 degrees below * 0.005) = 14.92 volts.


              For every 1º F above 77º F subtract 0.0028 volts per cell or for every 1º C above 25º C subtract 0.005 volts per cell to the charger voltage setting.

              • 1: A 12 volt battery @ 85º F. The recommended charger voltage at 77º F is 14.8 volts. The adjusted charging voltage is 14.8 – (6 cells * 8 degrees above * 0.0028) = 14.67 volts.
              • 2: A 12 volt battery @ 29.5º C. The recommended charger voltage at 25º C is 14.8 volts. The adjusted charging voltage is 14.8 – (6 cells * 4.5 degrees above * 0.005) = 14.67 volts.

5. Is there a maximum temperature for charging my batteries?
When charging lead acid batteries, the temperature should not exceed 120ºF. At this point the battery should be dissconnected from all charging sources and loads in order to cool before resuming the charge process.


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Battery Recycling

1. Are lead acid batteries recyclable?
Lead acid batteries are 97% recyclable. Lead is the most recycled metal in the world today. All the lead purchased by Trojan Battery Company for grid and small parts casting is recycled lead. The plastic containers and covers of old batteries are neutralized, reground and used in the manufacture of new battery cases. The electrolyte can be processed for recycled wastewater uses. In some cases, the electrolyte is cleaned and reprocessed and sold as battery grade electrolyte. In other instances, the sulfate content is removed as Ammonia Sulfate and used in fertilizers. The separators are often used as a fuel source for the recycling process.

2. Where do I recycle my old batteries?
Old batteries may be returned to the battery retailer, automotive service station, a battery manufacturer or other authorized collection centers for recycling. If you are not sure where to take your spent batteries, call your local Trojan dealer for assistance.

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Battery Myths

1. What are some common myths associated with batteries?

            • Half of a non-buffered aspirin in each cell and then a fast charge breaks up sulfation and extends battery life- Aspirin forms ascetic acid which attacks the positive grid and active material.
            • Storing a battery on concrete will discharge it quicker- Long ago, when battery cases were made out of natural rubber, this was true. Now, however, battery cases are made of polypropylene or other modern materials that allow a battery to be stored anywhere. A battery’s rate of discharge is affected by its construction, its age, and the ambient temperature. The main issue with storing on concrete is that if the battery leaks, the concrete will be damaged.
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