Internal resistance of the battery / rechargeable battery - an important parameter of the power source

What is the internal resistance of a battery?

As we have already explained in our glossary, the internal resistance in batteries and accumulators determines the self-resistance of a cell. Each battery acts to a certain extent like a standard resistor-resistor, where the current flowing through them causes a certain voltage drop. The larger the battery resists, the greater the voltage drop it causes and, as a result, the voltage that physically goes to our receiver is always lower than the voltage measured on the battery outside the device (without load).

This lower voltage during operation will be very important to us. After all, a typical device refuses to work when the voltage drops to a specific, sufficiently low level, so in the case of a battery with high resistance, it may refuse to work prematurely. In addition, in many devices, the quality of operation of a given device depends on the voltage level (at higher voltage, the devices often operate with more power - the motors work faster, the flashlight shines brighter, the toy drives faster, etc.).

Batteries with higher resistance, even when exhibiting the same mAh capacity, generate a higher voltage drop at the terminals when discharging – according to Ohm's basic law. New batteries or rechargeable batteries differ in this parameter. In addition, an increase in internal resistance is a natural phenomenon of battery wear and tear as they are used and discharged. What is very important, this parameter deteriorates even on unused batteries - it is one of the symptoms of cell aging. This is a very negative phenomenon, as it very often leads to premature and unexpected shutdown of the device. Energy losses related to the internal resistance of the battery are dissipated in the form of heat directly on the battery and its contacts. High internal resistance can lead to overheating of batteries in demanding devices - e.g. flash units. In general, the conclusion is that the lower the resistance, the better. A rechargeable battery, a battery with low resistance, is able to effectively and safely give off higher current values.

Next to capacity, it is one of the most important and important parameters determining the performance of a battery or accumulator, the existence of which not everyone is aware of.

How to check the internal resistance of our batteries or rechargeable batteries?

The measurement procedure used by different manufacturers is not consistent and usually the resistance values given in the technical data sheets are not comparable with each other. Therefore, it is worth taking such measurements on your own.

A typical measurement procedure involves (A) measuring the voltage of a cell that is at least half charged, under stable, repeatable conditions (with little or no load), then loading it (B) with an additional, specified current value, and quickly (usually within a few seconds) re-reading the voltage value (C). The difference in the measured voltages A-C divided by the value of the additional load - current B gives us the value of the internal resistance of the cell.

The results obtained even on the same battery will vary depending on the degree of charge of a given cell (the highest, worst results are achieved by discharged cells). They will also usually be higher (worse) the higher the load/current B we use to measure or later measure the voltage drop (C).

Therefore, when comparing these values, it is very important that the procedure is the same each time.

Independent, "manual" measurement of internal resistance can be troublesome, which is why chargers come to the rescue here, as they can perform such a measurement automatically and repeatably.

There are only a few chargers on the market that measure these values correctly. The few exceptions are everActive chargers (e.g. NC-3000 model) and Xtar chargers (e.g. VP4+ Dragon).

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