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More Battery Info

Deep Cycle Battery Maintenance

Brought to you by Trojan Battery Company

Expanded Edition

Now Includes Flooded, Gel and AGM technology

Testing Watering
Cleaning Storage
Charging Equalizing
System Configuration Battery Terms Explained


Simple Steps For Longer Battery Life

Naturally, you want to get maximum value from your battery investment. We’re here to help you do exactly that. Trojan Battery Company has manufactured lead acid batteries for more than three generations.

Our experience shows that the key factor in achieving optimum performance and long life is a solid battery care and maintenance program, as outlined in this brochure.

Following the simple procedures we’ve described is sure to provide the biggest returns on your battery investment.



Trojan recommends the following basic equipment for use in battery care and maintenance.



• Wrench

• Distilled Water

• Voltmeter

• Hydrometer


• Post Cleaner

• Baking Soda

• Petroleum Jelly

• Goggles and Gloves

CAUTION: Always wear protective clothing, gloves, and goggles when handling batteries and electrolyte.



1. Examine the outside appearance of the battery.

• Look for cracks in the container.

• The top of the battery, posts and connections should be free of dirt, fluids and
    corrosion. (If batteries are dirty, see Cleaning section )

• Replace any damaged batteries.

2. Any fluids on or around the battery may indicate that electrolyte is spilling, leaching or leaking out

• Leaking batteries must be replaced.

3. Check all battery cables and connections.

• Look closely for loose or damaged parts.

• Replace any cable that is broken or frayed.

4. Tighten all wiring connections to the proper specification (see below). Be sure there is good contact with the terminals


WARNING: Do not over-tighten terminals. Over-tightening can result in post breakage, post meltdown or fire.


Proper Torque Values for Connection Hardware 
Flooded 65 to 75 in-lbs Gel or AGM 90 to 100 in-lbs


Specific Gravity Testing

(Flooded batteries only)

1. Do not add water yet.

2. Fill and drain the hydrometer 2-4 times before drawing a sample from the battery.

3. Have enough sample electrolyte in the hydrometer to completely support the float

4. Take a reading, record it and return the electrolyte to the cell.

5. Check all cells in the battery, repeating the steps above

6. Replace vent caps and wipe off any electrolyte that might have been spilled

7. Correct the readings to 80º F.

• Add .004 to readings for every 10º above 80º F.

• Subtract .004 for every 10º below 80º F. 

8. Check the state of charge using the the following Table


The readings should be at or above the factory specification of 1.277 +/-.007. If any specific gravity reading registers low, follow these steps

1. Check and record voltage level(s).

2. Put batteries on a complete charge

3. Take specific gravity readings again.

If any specific gravity reading still registers low, follow these steps.

1. Check voltage level(s).

2. Perform equalization charge (See Equalizing section.)

3. Take specific gravity readings again.

If any specific gravity reading still registers lower than the factory specification, one or more of these conditions may exist.

1. The battery is old and nearing end of life

2. The battery was left discharged too long

3. Electrolyte was lost due to spillage.

4. A weak or bad cell is developing.

5. The battery was over-watered prior to testing

Batteries in conditions 1-4 should be taken to a specialist for further evaluation, or retired from service.


Open-Circuit Voltage Testing

For accurate voltage readings, batteries must remain idle (no charging, no discharging) for at least 6 hours and preferably 24 hours

1. Disconnect all loads from the batteries

2. Measure the voltage with a DC voltmeter.

3. Correct the readings to 80ºF

• Add .028/cell for every 10º above 80ºF.

• Subtract .028/cell for every 10º below 80ºF. 

4. Check the state of charge with the Table below. 

5. Charge the battery if it registers 0-70% charged.


If battery registers below Table values, these conditions may exist

1 The battery was left in a state of discharge too long.

2. The battery has a bad cell.

Batteries in these conditions should be taken to a specialist for further evaluation, or retired

from service.






6.37 12.73
90 1.258 6.31 12.62
80 1.238 6.25 12.50
70 1.217 6.19 12.37
60 1.195 6.12 12.24
50 1.172 6.05 12.10
40 1.148 5.98 11.96
30 1.124 5.91 11.81
20 1.098 5.83 11.66
10 1.073 5.75 11.51

State of charge as related to specific gravity and open-circuit voltage


(Flooded batteries only)

Water should always be added after fully charging the battery. Prior to charging, there should be enough water to cover the plates If the battery has been discharged (partially or fully), the water level should also be above the plates.

Important things to remember:

1 Do not let plates get exposed to air.

2. Do not fill the water all the way up to the cap.

3. Do not use water with a high mineral content.

4. Use only distilled or deionized water.


CAUTION: The electrolyte is a solution of acid and water, so skin contact should be avoided.



1. Open the vent caps and check the electrolyte level; the minimum level is to the top of the plates

2. If there is no water visible, add just enough to cover the plates.

3. Put batteries on a complete charge before adding any more water. (See Charging section.)

4 Once charging is completed, open the vent caps and check the electrolyte level.

5. Add water until the electrolyte level is 1/8" below the bottom of the fill well.

6. Clean, replace, and tighten all vent caps


WARNING: Never add acid to a battery.



1. Check that all vent caps are tight

2. Clean the battery top with a cloth or brush and a solution of baking soda and water.

• Do not allow any cleaning solution, or other foreign matter to get inside the battery.

3. Rinse with water and dry with a clean cloth

4. Clean battery terminals and the inside of cable clamps with a post and clamp cleaner.

5. Reconnect the clamps to the terminals and thinly coat them with petroleum jelly.

6. Keep the area around batteries clean and dry.



Important things to avoid:

1. Freezing – Avoid locations where freezing temperatures are expected. Keeping batteries at a high state of charge also prevents freezing.

2. Heat – Avoid direct exposure to heat sources, such as radiators or space heaters. Temperatures above 80º F accelerate the battery's self-discharge characteristics.



1. Completely charge the battery before storing

2. Store the battery in a cool, dry location, protected from the elements.

3. During storage, monitor the specific gravity (flooded) or voltage

• Stored batteries should be given a boost charge when they show a 70% charge or less. (See Table previous page.)

4. Completely charge the battery before re-activating

5. For optimum performance, equalize the batteries (flooded) before putting them back into service (See Equalizing section.)



Correctly charging batteries requires administering the right amount of current at the right voltage. Most charging equipment automatically regulates these values. Some chargers allow the user to set these values. For proper charging, refer to the instructions that came with your charging equipment.


Important things to remember:

1. Become familiar with and follow the instructions from the charger manufacturer.

2. Batteries should be charged after each period of use

3. Lead acid batteries do not develop a memory and need not be fully discharged before recharging.

4. Charge only in well-ventilated areas. Keep sparks or flames away from a charging battery.

5. Verify charger voltage settings are correct.

6. Check water level. (See Watering section.)

7. Tighten all vent caps before charging

8. Do not overcharge or undercharge the batteries

9. Never charge a frozen battery.

10. Avoid charging at temperatures above 120º F.



(Flooded batteries only)


WARNING: Do not equalize Gel or AGM batteries.


Equalizing is an overcharge performed on flooded lead acid batteries after they have been fully charged It helps eliminate stratification and sulfation, two conditions that can reduce the overall performance of a battery.

Trojan recommends equalizing only when low or wide ranging specific gravity (+/-.015) is detected after fully charging a battery.


1. Verify that batteries are the flooded type.

2. Remove all loads from the batteries.

3. Connect battery charger.

4. Set charger for the equalizing voltage.

5. Start charging batteries.

6. Batteries will begin gassing and bubbling vigorously.

7. Take specific gravity readings every hour.

8. Equalization is complete when specific gravity values no longer rise during the gassing stage.


NOTE: Many chargers do not have an equalization setting, so this procedure cannot be used.

How To Increase System Power

Two or more batteries can be easily connected to boost your system's voltage and/or capacity. There are three methods to obtain additional voltage and/or capacity, as described below

To increase voltage, connect batteries in series

Battery System: 12 Volt, 225 AH 
Using Two T-105 Deep Cycle Batteries 
(6 Volts, 225 AH)


To increase amp-hour capacity, connect batteries in parallel.

Battery System: 6 Volt, 450 AH 
Using Two T-105 Deep Cycle Batteries 
(6 Volts, 225 AH)

To increase both voltage and amp-hour capacity, connect batteries

in series/parallel.

Battery System: 12 Volt, 450 AH 
Using Four T-105 Deep Cycle Batteries 
(6Volts, 225 AH)

Suggested Maximum Ampacity for Copper Wire

Wire Gauge Size
14 25
12 30
10 40
8 55
6 75
4 95
2 130
1 150
1/0 170
2/0 265
4/0 360


Ampacity is the ultimate safe current carrying capacity of the wire before damage occurs to the insulation. These are suggested ampacities. Refer to the National Electrical Code or your local code for correct wire size usage.

NOTE: These systems can also be configured using 12 volt batteries. It is not recommended that you mix batteries of different voltages within the same system.

Battery Terms Explained

1. Active Material - In the positive plates, the active material is lead dioxide In the negative, it's metallic sponge lead. When a circuit is created, these materials react with sulfuric acid during charging and discharging

2. Ampere (Amp) - A unit of measurement for the electron flow or current through a circuit.

3. Ampere-Hour (Amp. Hr., AH) - A unit of measure for a battery's electrical storage capacity, calculated by multiplying the current in amperes by the time in hours (Example A battery which delivers 5 amps for 20 hours provides 5 amps x 20 hours = 100 AH of capacity.)

4. Capacity Rating - The time in minutes that a new, fully charged battery will deliver 25 amperes or 75 amperes at 80º F and maintain a terminal voltage equal to or greater than 1 75 volts per cell.

5. Cell - The basic current-producing unit in a battery. It consists of a set of positive plates, negative plates, electrolyte, separators and casing. (A 12-volt deep cycle battery has 6 cells.) 

6. Circuit - The path followed by a flow of electrons. A closed circuit is a complete path An open circuit, or short, has a broken path. 

7. Cycle - One discharge of a battery plus one recharge. 

8. Depth of Discharge (DOD) - The percentage of capacity actually removed from a battery compared to the total rated capacity. 

9. Electrolyte - In a deep cycle battery, it is a dilute solution of sulfuric acid and water. Hydrometer – A tool used to measure the specific gravity of the electrolyte solution. 

10. Equalization - An overcharge performed on flooded lead-acid batteries after they have been fully charged This maintenance step helps eliminate stratification and sulfation

11. Lifetime Energy Units™ (LEUs) - The number of Kilowatt-hours of energy a battery delivers over its useful life

12. Ohm (Q) - A unit of measurement for electrical resistance within a circuit.

13. Open Circuit Voltage - The voltage of a battery when there is no load attached (not receiving or delivering energy) This measurement is best taken when the battery has been at rest for at least 6 hours.

14. Power Inverter - An electronic device that converts direct current (DC) power from a battery into standard alternating current (AC) house power.

15. Primary Battery - An energy storage device that can deliver energy but cannot be recharged (i e., disposable flashlight battery)

16. Secondary Battery - An energy storage device than can deliver energy and can be recharged (i.e., automotive or deep cycle battery)

17. Separator - A divider made of porous material that is placed between the positive and negative plates in a battery cell and allows current to flow through it, while preventing direct contact between the plates which would cause a short circuit

18. Specific Gravity (S.G.) - A method of measuring the strength of battery electrolyte by comparing its density to that of pure water.

19. Stratification - A condition where the concentration of acid is greater at the bottom of the battery than at the top

20. Sulfation - The formation of lead sulfate on the positive and negative electrodes

21. Volt (V) - A unit of measurement for electrical potential within a circuit.

22. Watt (W) - A unit of measurement for electrical power.

23. Watt Hour (Wh) - A unit of measurement for electrical power for a certain period of time.

Look for LEUs™ on our labels to make deep cycle battery comparison simple

Pioneered by Trojan, Lifetime Energy Units™ are an accurate convenient way to compare the relative value of one deep cycle battery to another. Simply stated LEUs signify the number of kilowatt-hours of energy a battery delivers over its useful life The bigger the number the more work the battery can perform. Yes it's that simple!

Comparing Batteries

Ordinary deep cycle batteries rapidly degrade. Over the long haul Trojan deep cycle batteries deliver more performance and value We call that difference the Trojan Advantage.




12380 Clark Street, Santa Fe Springs, CA 90670

Phone: 562-946-8381, 800-423-6569, Fax: 562-906-4033

In Georgia: 770-981-8674, 800-246-2550, Fax: 770-981-7717