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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

When one amp of current passes through a circuit with zero ohms (the unit of measure for resistance) of resistance, no voltage drop occurs. Even when the circuit current increases to 200 amps through zero ohms, still no voltage drop occurs. The amount of resistance encountered by a current causes a voltage drop. Ohm's Law explains how small resistance values can cause severe voltage drops. The basic form of Ohm's Law is E = I x R, where the current, I in amps, is multiplied by the resistance, R in ohms, to equal the voltage drop, E in volts. To see the affect resistance has on voltage we use Ohm's Law and solve for voltage as shown here by the following equation: I(Amps) X R(Ohms) = E(Voltage).

By substituting different values for resistance, we can see small resistances can cause significant voltage drop problems, especially in high amperage systems as shown below:

1 Amp X 0(Ohms) = 0 (no voltage drop)
200 Amp X 0(Ohms) = 0 (no voltage drop)
1 Amp X 1 Ohm = 1.0 volt dropped
200 Amp X 0.01 Ohm = 2.0 volt dropped
200 Amp X 0.02 Ohm = 4.0 volt dropped


The Society of Automotive Engineers, S.A.E., has established the maximum voltage drops for common electrical circuit cables and connections. The acceptable voltage drops are shown below:

Voltage Drop (Volts) American Wire Size Current Component Application
0.01-.09 16 - 20 1-20 Computer Connections, Low Current Accessories
0.1-.2 4 - 14 20-100 Alternators, High Current Accessories
0.2 00 - 4 100+ Battery/Starter Cables
0.2-.3 N/A 100+ Heavy Duty Switches, Solenoids

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

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