Need for IR test of a UPS battery

Last Updated on: 27-02-2023

In the event of power failure, UPS or Uninterrupted Power Supply provides emergency power backup for your mission-critical applications. A UPS System protects your essential equipments from power surges, brownouts, blackouts, and power transients. UPS systems predominantly rely on batteries as their source of power, hence it is an utmost necessity to periodically test UPS battery IR. 

What is IR? 

IR means Internal Resistance of batteries. The internal resistance (IR) of a battery is defined as the opposition to the flow of current within the battery. Two primary components impact the internal resistance of a battery; they are electronic resistance and ionic resistance. 

The internal resistance is measured in ohm (Ω). The value of internal resistance varies depending on various factors, such as battery size, a cathode electrode, anode electrode, separator, electrolyte, temperature, and state of charge (SOC) of the battery. 

Ideally, a battery should have 0Ω internal resistance. In practice, however, batteries will have some internal resistance. It is because the materials used in the batteries are not perfect conductors. They will have some opposition, which contributes to the internal resistance of the battery. 

Why UPS Battery IR Test is Important  

Regular IR testing of UPS batteries can aid you in identifying and addressing battery performance. Internal resistance is the most important factor that provides valuable information about a battery’s health. Internal resistance readings help to identify problems with inter-cell connections, and corrosion of terminals. A high reading of battery IR may indicate that the UPS battery life is approaching its end of usefulness. 

What causes the IR to increase? 


A battery must be re-charged immediately after a discharge. If the recharging process is not started immediately, then the sulfation on the electrodes will lead to high internal resistance. This sulfation shall reduce the property of charge acceptance leading to premature battery failure. 


If a battery is subjected to an operating temperature higher than the recommended temperature, then the positive grid inside the batteries will start corroding. It will also lead to premature battery failure. 


Due to ageing, the electrodes can change in porosity, crystal structure, and chemical composition, increasing the battery’s internal resistance. 


Certain electrolyte additives will have parasitic corrosion issues that might affect the internal resistance of the battery. 

Understanding the role of the internal resistance of batteries and the need for IR test of a UPS battery is required, will help you make better decisions in terms of preventive maintenance and support required for UPS, thereby ensuring uninterrupted workflow. 

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