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Phone: 503-362-2684
Fax: 503-362-2787

2725 Portland Rd. NE,
Salem, OR 97301


Battery School

General Battery Care Procedures

General deep cycle battery care procedures

Reasons Why Batteries Fail

General Difference Between Gel and Wet Batteries

State of Charge and Sulfation

Connect Your Batteries for Optimum Efficiency

Just A Little Corrosion Causes Big Voltage Drops

Don't Be Misled By Battery Ratings

Which Deep Cycle Battery Do I Choose?

Daily Amphere-Hour Consumption For Your RV

Safety Tips on Charging Batteries

Determining When A Battery is Fully Charged

  1. The best way to determine when a battery is fully charged is to check specific gravity of each cell with a hydrometer. (background--As the battery discharges, the sulfuric acid content of the electrolyte solution is reduced, leaving water. Therefore, the specific gravity decreases as the battery is discharged).
  2. Specific gravity measurements show the state of charge of a battery according to the following chart.

    State of Charge Specific Gravity
    100% 1.265
    75% 1.225
    50% 1.190
    25% 1.155
    Discharged 1.120

    When a battery is below 75% of full charge, sulfation (or hardening) of the plates begins to occur and permanent battery damage may result. It is important to keep batteries as fully charged as possible.


  1. Hold the hydrometer vertically so the float is free and does not touch the inner walls of the barrel.
  2. To increase accuracy of the hydrometer, draw electrolyte into the bulb a few times until the hydrometer parts reach the same temperature as the electrolyte.
  3. Hold the hydrometer so that liquid is level in barrel and at eye level.
  4. Read specific gravity from the scale on the calibrated float at the point where the surface of the liquid crosses the float.
  5. Check each individual battery cell. Specific gravity should not vary more than .050 or "50", points between cells. If a cell varies more than 50 points, charge again. If this difference still remains, replace the battery.
  6. Measure the electrolyte temperature with a thermometer for best accuracy. Then correct hydrometer readings for electrolyte temperature (see hydrometer instructions for details on temperature compensation ... normally, in the summer this does not have to be done given our climate in the Northwest).

Why Are My Batteries Discharged

What is the difference between series battery connections and parallel battery connections and how do they increase battery capacity and voltage?

Jump start procedures

Preparing your batteries for winter

Advantages and Disadvantages of using two 12 volt batteries connected in parallel or two 6 volt batteries connected in series.

Testing the battery