USA Battery Sales
Call: 888-737-5681
Please read the following:
Before getting started:
? Make sure you know your system voltage, battery compartment size (length, width and height) and your energy needs.
? Determine whether you want to use a deep cycle flooded, Deep-Cycle Gel or Cycling AGM battery.

Step 1: Determine your battery voltage and how many to use
1-1 Based on your system voltage, you must first decide which battery is needed and how many to use in order to meet your requirements. For example, you may connect a series of eight 6V batteries, six 8V batteries or four 12V batteries for a 48-volt system. The size of your battery compartment, your performance requirements and costs may limit your options.

1-2 Make sure there is enough space between batteries to allow for minor battery expansion that occurs during use and to allow proper airflow to keep battery temperature down in hot environments.

TIP: Connecting batteries in series does not increase the capacity of the batteries; it simply increases the overall voltage to meet your system requirements. Once your voltage requirements are met, if space allows you can double the batteries in a parallel connection?thereby doubling your battery capacity. See diagrams below.

Series Connect
To increase voltage, connect batteries in series. This will not increase the system capacity.

Example :
Two T-105, 6V Batteries rated at 225AH Connected in Series

System Voltage: 6V + 6V = 12V
System Capacity = 225AH

To increase voltage,
connect batteries in series.
Parallel Connect
To increase capacity, connect batteries in parallel. This will not increase the system voltage.

Example :
Two T-105, 6V Batteries rated at 225AH Connected in Parallel

System Voltage: 6V
System Capacity = 225AH + 225AH = 450AH

To increase amp-hour capacity,
connect batteries in parallel.
Series/Parallel Connect

To increase both voltage and capacity, connect additional batteries in series and parallel.

Example :
Four T-105, 6V Batteries rated at 225AH Connected in Series/Parallel

System Voltage: 6V + 6V = 12V
System Capacity = 225AH + 225AH = 450AH

To increase both voltage and
amp-hour capacity, connect
batteries in series/parallel.

Step 2: Choose your best battery model
2-1 When choosing your battery model, first consider your battery compartment space as this may limit your options. Within your size restrictions you may have several battery options to choose from. For example, you can use a T-105 or T-125 in the same space, as they are the exact same physical size. The difference between these batteries is the amount of energy they have to offer.

2-2 Next consider your energy needs. If replacing an existing battery, use it as a reference point. If your old battery provided enough energy, it can be replaced with a similar capacity battery. If you need more energy you can size up, or if you need less energy you can size down.

TIP: If you do not know what battery to use, contact your equipment manufacturer for their recommended battery specification. Trojan Battery also offers outstanding technical support provided by full-time applications engineers to help you select your ideal batteries.

Step 3: Select your best terminal
3-1 Finally determine which terminal option best meets your needs based on the type of cable connections you plan to use. Look for the terminal(s) available for the battery you have selected. (Please see the back page of this guide for available terminals to make your selection.)

TIP: Make sure you use the proper cable size when connecting your batteries so that you do not overheat your connections.
Battery Type
Lead acid batteries are generally classified by application (what they are used for) and by construction (how they are made). The primary application is automotive in which the battery is used for starting and lighting. Deep cycle is another major application but is usually broken down into more specific applications such as RV, golf cars, renewable energy, and marine.

There are two popular construction types: flooded batteries (wet) and VRLA batteries (Valve Regulated Lead Acid). In the flooded types, the electrolyte is a solution of sulfuric acid and water that can spill out if the battery is tipped over. In VRLA batteries, the electrolyte is suspended in a gel or a fiberglass-mat (AGM technology), allowing these batteries to be mounted in a variety of positions.

Before getting started, be sure to identify the type of battery involved. This section addresses the charging and maintenance for both flooded and VRLA batteries.
There are many tools that may help in properly caring for and maintaining batteries. Below is a list of basic items that Trojan recommends for this task:

Recommended Equipment:

  • Wrench
  • Distilled Water
  • Voltmeter
  • Hydrometer
  • Post Cleaner
  • Baking Soda
  • Vaseline
  • Goggles & Gloves

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

Batteries should be carefully inspected on a regular basis in order to detect and correct potential problems before they can do harm. It is a great idea to start this routine when the batteries are first received.

Inspection Guildlines:

1. Examine the outside appearance of the battery.

  • Look for cracks in the container.
  • The top of the battery, posts, and connections should be clean, free of dirt, fluids, and corrosion. If batteries are dirty, refer to the Cleaning section for the proper cleaning procedure.
  • Repair or replace any damaged batteries.

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

  • Leaking batteries must be repaired or replaced.

3. Check all battery cables and their connections.

  • Look closely for loose or damaged parts.
  • Battery cables should be intact; broken or frayed cables can be extremely hazardous.
  • Replace any cable that looks suspicious.
4. Tighten all wiring connections to the proper specification (see below). Make certain there is good contact with the terminals.

Proper Torque Values for Connection Hardware:

Flooded Automotive 50-70 in-lbs
Side 70-90 in-lbs
Wingnut 95-105 in-lbs
LPT 95-105 in-lbs
Stud 120-180 in-lbs
LT 100-120 in-lbs
VRLA Button 90 to 100 in-lbs
LT 100-120 in-lbs

WARNING: Do not overtighten terminals. Doing so can result in post breakage, post meltdown, or fire.


Visual inspection alone is not sufficient to determine the overall health of the battery. Both open-circuit voltage and specific gravity readings can give a good indication of the battery's charge level, age, and health. Routine voltage and gravity checks will not only show the state of charge but also help spot signs of improper care, such as undercharging and over-watering, and possibly even locate a bad or weak battery. The following steps outline how to properly perform routine voltage and specific gravity testing on batteries.

I. Specific Gravity Test
(Flooded batteries only)

1. Do not add water at this time.

2. Fill and drain the hydrometer 2 to 4 times before pulling out a sample.

3. There should be enough sample electrolyte in the hydrometer to completely support the float.

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

5. To check another cell, repeat the 3 steps above.

6. Check all cells in the battery.

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

8. Correct the readings to 80o F:

  • Add .004 to readings for every 10o above 80o F
  • Subtract .004 for every 10o below 80o F.
9. Compare the readings.

10. Check the state of charge using Table 1.

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

1. Check and record voltage level(s).

2. Put battery(s) on a complete charge.

3. Take specific gravity readings again.

If any specific gravity readings still register low then follow the steps below.

1. Check voltage level(s).

2. Perform equalization charge. Refer to the Equalizing section for the proper procedure.

3. Take specific gravity readings again.

If any specific gravity reading still registers lower than the factory specification of 1.277+/- .007 then one or more of the following conditions may exist:

1. The battery is old and approaching the end of its life.

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

3. Electrolyte was lost due to spillage or overflow.

4. A weak or bad cell is developing.

5. Battery was watered excessively previous to testing.

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

II. Open-Circuit Voltage Test
For accurate voltage readings, batteries must remain idle (no charging, no discharging) for at least 6 hrs, preferably 24 hrs.

1. Disconnect all loads from the batteries.

2. Measure the voltage using a DC voltmeter.

3. Check the state of charge with Table 1.

4. Charge the battery if it registers 0% to 70% charged.

If battery registers below the Table 1 values, the following 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.

TABLE 1. State of charge as related to specific gravity and
open circuit voltage

Percentage of Charge
Specific Gravity Corrected to
80o F
Open-Circuit Voltage

There are six simple steps in testing a deep cycle battery-inspect, recharge, remove surface charge, measure the state-of-charge, load test, and recharge. If you have a non-sealed battery, it is highly recommended that you use a good quality temperature compensated hydrometer.
 A hydrometer is a float type device used to determine the state-of-charge by measuring the specific gravity of the electrolyte in each cell. It is a very accurate way of determining a battery's state-of-charge and its weak or dead cells.
 To troubleshoot charging or electrical systems or if you have a sealed battery, you will need a digital voltmeter with 0.5% or better accuracy. 
 Analog voltmeters are not accurate enough to measure the millivolt differences of a battery's state-of-charge or the output of the charging system.
 The purchase of a battery load tester is optional; if you use a golf cart or electric trolling motor every day, buy one.


Visually inspect for obvious problems.
 For example, is there a loose or broken alternator belt, electrolyte levels BELOW the top of the plates, corroded or swollen cables, corroded terminal clamps, dirty or wet battery top, loose hold-down clamps, loose cable terminals, or leaking or damaged battery case?
 If the electrolyte levels are low in non-sealed batteries, allow the battery to cool and add DISTILLED water to the level indicated by the battery manufacturer. If this is not indicated, use 1/4 inch (7 mm) BELOW the bottom of the plastic filler tube (vent wells).
 The plates need to be covered at all times. Avoid OVERFILLING, especially in hot climates, because heat will cause the electrolyte to expand and overflow.


Recharge the battery to 100% state-of-charge.
 If the battery has a difference of .03 specific gravity reading between the lowest and highest cell, then you should equalize it. (Please see Section 6.)


Surface charge is the uneven mixture of sulfuric acid and water within the surface of the plates as a result of charging or discharging. It will make a weak battery appear good or a good battery appear bad. You need to eliminate the surface charge by one of the following methods:

3.1. Allow the battery to sit for four to twelve hours to allow for the surface charge to dissipate.

3.2. Apply a load that is 33% of the ampere-hour capacity for five minutes and wait five to ten minutes.

3.3. With a battery load tester, apply a load of at least one half the battery's CCA rating for 15 seconds and wait five to ten minutes.


If the battery's electrolyte is above 110o F (43.3o C), allow it to cool.
 To determine the battery's state-of-charge with the battery's electrolyte temperature at 80o F (26.7o C), use the following table. The table assumes that a 1.265 specific gravity reading is a fully charged, wet, lead-acid battery.
 For other electrolyte temperatures, use the Temperature Compensation table below to adjust the Open Circuit Voltage or Specific Gravity readings.
 The Open Circuit Voltage will vary for gel cell and AGM type batteries so check the manufacturer's specifications.

Digital Voltmeter Open Circuit Voltage Approximate State-of-Charge Hydrometer Average Cell Specific Gravity Electrolyte Freeze Point
12.65 100% 1.265 -75o F (-59.4o C)
12.45 75% 1.225 -55o F (-48.3o C)
12.24 50% 1.190 -34o F (-36.7o C)
12.06 25% 1.155 -16o F (-26.7o C)
11.89 Discharged 1.120 -10o F (-23.3o C)

Electrolyte Temperature Fahrenheit Electrolyte Temperature Celsius Add or Subtract to Hydrometer's SG Reading Add or Subtract to Digital Voltmeter's Reading
160o 71.1o +.032 +.192
150o 65.6o +.028 +.168
140o 60.0o +.024 +.144
130o 54.4o +.020 +.120
120o 48.9o +.016 +.096
110o 43.3o +.012 +.072
100o 37.8o +.008 +.048
90o 32.2o +.004 +.024
80o 26.7o 0 0
70o 21.1o -.004 -.024
60o 15.6o -.008 -.048
50o 10o -.012 -.072
40o 4.4o -.016 -.096
30o -1.1o -.020 -.120
20o -6.7o -.024 -.144
10o -12.2o -.028 -.168
0o -17.8o -.032 -.192


Electrolyte temperature compensation will vary depending on the battery manufacturer's recommendations. If you are using a NON-temperature compensated HYDROMETER, make the adjustments indicated in the table above. For example, at 30 o F (-1.1o C), the specific gravity reading would be 1.245 for a 100% state-of-charge. At 100 o F (37.8 o C), the specific gravity would be 1.273 for 100% state-of-charge. This is why using a temperature compensated hydrometer is highly recommended and more accurate. If you are using a DIGITAL VOLTMETER, make the adjustments indicated in the table above. For example, at 30 o F (-1.1o C), the voltage reading would be 12.53 for a 100% state-of-charge. At 100 o F (37.8 o C), the voltage would be 12.698 for 100% state-of-charge.

For non-sealed batteries, check the specific gravity in each cell with a hydrometer and average the readings.
 For sealed batteries, measure the Open Circuit Voltage across the battery terminals with an accurate digital voltmeter.
 This is the only way you can determine the state-of-charge. Some batteries have a built-in hydrometer, which only measures the state-of-charge in ONE of its six cells.
 If the built-in indicator is clear or light yellow, then the battery has a low electrolyte level and should be refilled and recharged before proceeding. If sealed, the battery should be replaced.

If the state-of-charge is BELOW 75%, using either the specific gravity or voltage test, or the built-in hydrometer indicates "bad" (usually dark), then the battery needs to be recharged BEFORE proceeding.
 You should also replace the battery if one or more of the following conditions occur:

4.1. If there is a .05 (sometimes expressed as 50 "points") or more difference in the specific gravity reading between the highest and lowest cell, you have a weak or dead cell(s).
 If you are really lucky, applying an EQUALIZING charge may correct this condition. (Please see Section 6.)

4.2. If the battery will not recharge to a 75% or more state-of-charge level or if the built-in hydrometer still does not indicate "good" (usually green, which is 65% state-of-charge or better).

If you know that a battery has spilled or "bubbled over" and the electrolyte has been replaced with water, you can replace the old electrolyte with new electrolyte and go back to Step 3.2 above.
 Battery electrolyte is a mixture of 25% sulfuric acid and distilled water. It is cheaper to replace the electrolyte than to buy a new battery.

4.3. If digital voltmeter indicates 0 volts, you have an open cell.

4.4. If the digital voltmeter indicates 10.45 to 10.65 volts, you probably have a shorted cell or a severely discharged battery. A shorted cell is caused by plates touching, sediment ("mud") build-up or "treeing" between the plates.


If the battery is fully charged or has a "good" built-in hydrometer indication, then you can test the capacity of the battery by applying a known load and measuring the time it take to discharge the battery until 20% capacity is remaining.
 Normally a discharge rate that will discharge a battery in 20 hours can be used. For example, if you have an 80-ampere-hour rated battery, then a load of four amps would discharge the battery in approximately 20 hours (or 16 hours down to the 20% level)
. New batteries can take up to 50 charge/discharge cycles before they reach their rated capacity. Depending on your application, batteries with 80% or less of their original capacity are considered to be bad.


If the battery passes the load test, you should recharge it as soon as possible to restore it to peak performance and to prevent lead sulfation.
Flooded batteries need water. More importantly, watering must be done at the right time and in the right amount or else the battery's performance and longevity suffers.
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. Keeping the water at the correct level after a full charge will prevent having to worry about the water level at a different state of charge.
Depending on the local climate, charging methods, application, etc. Trojan recommends that batteries be checked once a month until you get a feel for how thirsty your batteries are.
Important things to remember:
1. Do not let the plates get exposed to air. This will damage (corrode) the plates.
2. Do not fill the water level in the filling well to the cap. This most likely will cause the battery to overflow acid, consequently losing capacity and causing a corrosive mess.
3. Do not use water with a high mineral content. Use distilled or deionized water only.
CAUTION: The electrolyte is a solution of acid and water so skin contact should be avoided.
Step by step watering procedure:
1. Open the vent caps and look inside the fill wells.
2. Check electrolyte level; the minimum level is at the top of the plates.
3. If necessary add just enough water to cover the plates at this time.
4. Put batteries on a complete charge before adding any additional water (refer to the Charging section).
5. Once charging is completed, open the vent caps and look inside the fill wells.
6. Add water until the electrolyte level is 1/8" below the bottom of the fill well.
7. A piece of rubber can be used safely as a dipstick to help determine this level.
8. Clean, replace, and tighten all vent caps.
WARNING: Never add acid to a battery.
Batteries seem to attract dust, dirt, and grime. Keeping them clean will help one spot trouble signs if they appear and avoid problems associated with grime.

1. Check that all vent caps are tightly in place.

2. Clean the battery top with a cloth or brush and a solution of baking soda and water.
  • When cleaning, 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 using a post and clamp cleaner.

  • Clean terminals will have a bright metallic shine.

5. Reconnect the clamps to the terminals and thinly coat them with petroleum jelly (Vaseline) to prevent corrosion.

6. Keep the area around batteries clean and dry.

Periods of inactivity can be extremely harmful to lead acid batteries. When placing a battery into storage, follow the recommendations below to insure that the battery remains healthy and ready for use.

NOTE: Storing, charging or operating batteries on concrete is perfectly OK.

The most important things to avoid:

1. Freezing. Avoid locations where freezing temperature is expected. Keeping a battery at a high state of charge will also prevent freezing. Freezing results in irreparable damage to a battery's plates and container.

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

Step by step storage procedure:

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. Batteries in storage should be given a boost charge when they show a 70% charge or less. See Table 1 in the Testing Section.

4. Completely charge the battery before re-activating.

5. For optimum performance, equalize the batteries (flooded) before putting them back into service. Refer to the Equalizing section for this procedure.

Charger Selection
Most deep cycle applications have some sort of charging system already installed for battery charging (e.g. solar panels, inverter, golf car charger, alternator, etc.). However, there are still systems with deep cycle batteries where an individual charger must be selected. The following will help in making a proper selection.

There are many types of chargers available today. They are usually rated by their start rate, the rate in amperes that the charger will supply at the beginning of the charge cycle. When selecting a charger, the charge rate should be between 10% and 13% of the battery's 20-hour AH capacity. For example, a battery with a 20-hour capacity rating of 225 AH will use a charger rated between approximately 23 and 30 amps (for multiple battery charging use the AH rating of the entire bank). Chargers with lower ratings can be used but the charging time will be increased.

Trojan recommends using a 3-stage charger. Also called "automatic", "smart" or "IEI" chargers, these chargers prolong battery life with their well programmed charging profile. These chargers usually have three distinct charging stages: bulk, acceptance, and float.
Charging batteries properly 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. Both automatic and manual equipment can present difficulties in charging. Tables 2 & 3 list most of the necessary voltage settings one might need to program a charger. In either case the original instructions for your charging equipment should also be referenced for proper charging. Here is list of helpful items to remember when charging.

1. Become familiar with and follow the instructions issued by 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 area. Keep sparks or flames away from a charging battery.

5. Verify charger voltage settings are correct (Table 2).

6. Correct the charging voltage to compensate for temperatures above and below 80o F. (Add .028 volt per cell for every 10o below 80o F and subtract .028 volt per cell for every 10o above 80o F)

Table 2. Charger Voltage Settings for Flooded Batteries
System Voltage
Charger Voltage Setting
Daily Charge

Table 3. Charger Voltage Settings for VRLA Batteries

Charger Voltage Setting
System Voltage
Daily Charge
13.8 - 14.4
27.6 - 28.2
41.4 - 42.3
55.2 - 56.4

7. Check water level (see the Watering section).

8. Tighten all vent caps before charging.

9. Prevent overcharging the batteries. Overcharging causes excessive gassing (water breakdown), heat buildup, and battery aging.

10. Prevent undercharging the batteries. Undercharging causes stratification.

11. Do not charge a frozen battery.

12. Avoid charging at temperatures above 120o F.

Additional VRLA Charging Instructions:

1. Become familiar with and follow the instructions issued by the charger manufacturer.

2. Verify charger has necessary VRLA setting.

3. Set charger to VRLA voltage settings (Table 3).

4. Do not overcharge VRLA batteries. Overcharging will dry out the electrolyte and damage battery.
Equalizing (Wet Batteries Only)
Equalizing is an overcharge performed on flooded lead acid batteries after they have been fully charged. It reverses the buildup of negative chemical effects like stratification, a condition where acid concentration is greater at the bottom of the battery than at the top. Equalizing also helps to remove sulfate crystals that might have built up on the plates. If left unchecked, this condition, called sulfation, will reduce the overall capacity of the battery.

Many experts recommend that batteries be equalized periodically, ranging anywhere from once a month to once or twice per year. However, Trojan only recommends equalizing when low or wide ranging specific gravity (+/- .015) are detected after fully charging a battery.

Step by Step Equalizing:

1. Verify the battery(s) are flooded type.

2. Remove all loads from the batteries.

3. Connect battery charger.

4. Set charger for the equalizing voltage (Check table 2 in the Charging section above).

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 can't be carried out.
Discharging batteries is entirely a function of your particular application. However, below is list of helpful items:

1. Shallow discharges will result in a longer battery life.

2. 50% (or less) discharges are recommended.

3. 80% discharge is the maximum safe discharge.

4. Do not fully discharge flooded batteries (80% or more). This will damage (or kill) the battery.

5. Many experts recommend operating batteries only between the 50% to 85% of full charge range. A periodic equalization charge is a must when using this practice.

6. Do not leave batteries deeply discharged for any length of time.

7. lead acid batteries do not develop a memory and need not be fully discharged before recharging.

8. Batteries should be charged after each period of use.

9. Batteries that charge up but cannot support a load are most likely bad and should be tested. Refer to the Testing section for proper procedure.
% Discharged
% Charged

General watering instructions:

  • Add water, never acid, to cells (distilled water only )
  • For fully charged standard deep cycle batteries, add water to the level of 1/8 below bottom of vent well (see diagram A below)
  • For fully charged Plus Series batteries, add water to the maximum water level indicator (see diagram B below)
  • If the batteries are discharged, only add water if the plates are exposed. Add just enough water to cover the plates, then charge the batteries. Once fully charged, add water to the proper level indicated above
  • After watering, secure vent caps back on batteries

Diagram A   Diagram B
diagram A     diagram B
Add water to 1/8" below bottom of the
vent well.