Battery Resistance – Temperature and Formula

Batteries are gadgets that we have come to depend on and use regularly. These useful devices transform chemical reactions into electrical energy. We use batteries in different gadgets every day. You will most probably get to use batteries in flashlights, cars, video game controllers, watches, kid’s toys, and so on.

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Different batteries are affected by cold or hot temperatures differently. Therefore, most ideal batteries, no matter what type usually have an internal resistance. The internal resistance will change with a temperature change. Apart from this, the internal resistance of a battery is also dependent on its capacity, size, age, chemical properties, separator efficiency, and discharge rate.

In this article, we discuss battery resistance versus temperature. We also look at battery resistance calculation and formula. Let’s get started.

Battery Resistance vs Temperature

We define internal battery resistance as the opposition to the flow of current within the battery. We have two basic components that will impact the internal resistance of a battery. These are electronic and ionic resistance which make up the total effective resistance. 

The ionic resistance can be defined as the resistance to current flow within the battery due to a variety of electrochemical factors. Factors such as electrolyte conductivity, electrode surface area, and ion mobility. An ionic resistance and polarization effects do occur more slowly than electronic resistance. On the other hand, electronic resistance is the resistivity of the actual materials that make up the batteries and how well they make contact with each other. Materials such as metal covers and internal components can cause an electronic resistance to occur very quickly. Such a reaction can be seen within a few seconds after a battery is placed under load.

The internal resistance of a battery gets lower when the temperature of a battery increases. The resistance will also rise during discharge. It does so due to the active materials within a battery being used. Take note that the rate of change during this discharge will not be consistent. Other factors will impact the rate of discharge including depth of discharge, battery chemistry, age of the battery, and drain rate.

Cold temperatures also affect the battery as it will cause the electrochemical reactions which take place within a battery to slow down. It will reduce ion mobility in the electrolyte causing the internal resistance to rise as temperatures drop. This will cause less current to be supplied because diffusion tends to slow down as the average kinetic energy of the molecules is reduced. Therefore, when the temperature continues reducing or going down, the metal resistance within the battery will continue to lower down but with a smaller effect as compared to the chemical effects.

Battery Resistance Calculation

Before you get to calculate the battery resistance, you must first know and understand Ohm’s Law. Ohm’s law is used to describe the primary relationship in a DC electrical circuit between current, voltage, and resistance. The name Ohm came from a German physicist, George Ohm. It was discovered and published in 1827. Therefore, ohm’s law states that current is directly proportional to the voltage across two points when it is passed through a conductor between the two points.

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To understand the law better, we use Ohm’s law triangle to calculate battery resistance. This triangle represents the relationship between three main components that exist in an electrical circuit. These are voltage (V) in Volts, current (I) in Amps, and resistance (R) in Ohms.

When and if you want to know the battery’s internal resistance, it is highly recommended to take your readings. You will do this with an open circuit and with your battery attached to a load. You are guaranteed to get the correct reading this way. To calculate battery resistance we use Ohm’s law formula which uses the current and the voltage to calculate the resistance. Therefore, when calculating resistance we will divide the voltage by the amps. That is; R = V/ I

For example, when you are given a battery that has a 20A current limit with a maximum voltage of 4.2V. Here we will use 19A to get a 1A margin. The calculation will be as follows;

R = 4.2V / 19A

R = 0.22

0.22 is a safe lower limit for a 20A battery. It provides the lowest current limit of the battery without fear of it exploding.

Battery Resistance Formula

The internal resistance of a battery is one of the most important factors which define the efficiency of a battery. As earlier stated the internal resistance is the amount of opposition caused by current flow. This resistance is usually offered by the batteries and cells as a response to the flowing current within them. We usually calculate and measure the internal resistance of a battery in Ohms.

You can easily calculate the internal resistance of a battery using a common formula. The simplest formula to use is below:

E = I (r + R)

Whereby; 

e is the electromotive force 

I is the current

R and r represent the internal resistance across both terminals.

Before you calculate the internal resistance of a battery, first consider the potential difference that may be between the battery’s terminals. You can easily find a battery’s internal resistance when you connect the terminals of a battery with a load.

There is also an alternative formula to use when calculating the internal resistance of a battery you can use the formula: e – V = Ir

This formula is used when the voltage and electromotive force are given when you are calculating the value of resistance and current within the battery.

Apart from this, you can also use the formula (e – V)/I =r. you will mostly use this formula when you are calculating the resistance to one of the battery's terminals. Therefore, when looking for the formula for calculating the internal resistance, it is upon you to regenerate it to fit a given situation. You first have to know at least two values for every formula mentioned above.

Conclusion

From the above formulas, you can calculate your power, current, and battery resistance. You will also be able to calculate the current that your coil will draw and the wattage amount. It is important to note that any increase in the battery resistance will mean the current and power will reduce. Any decrease in resistance will lead to a current and power increase. Knowing these effects and that you are bound to get a low resistance from the continuous discharge rate of a battery, you will be able to practice safe battery handling and adjust the power at the coil.