How To Check The UPS Battery Condition

In hyperscale data centers that require extremely high reliability, it is very inadequate to judge the quality of UPS batteries by simply taking the voltage. Relying solely on voltage readings is deceptive, as it tends to mask the real chemical decay inside the battery. A complete battery health assessment must follow a “three-level diagnostic protocol”.

Firstly, conduct a meticulous appearance inspection to see if the case is bulging, or if the terminals are leaking or corroded. Secondly, use a professional tester to accurately measure the internal resistance (IR), because for VRLA batteries, an increase of 20-25% of the internal resistance over the reference value is the most reliable early warning signal for SOH decline. Thirdly, perform a controlled discharge test or load test. During a simulated power failure, verify that the actual capacity of the battery meets the nominal value. For infrastructure seeking high availability, the kind of manual “snapshot” testing done once or twice a year is not only time-consuming, but also extremely risky. Now the industry’s gold standard has shifted to automated Battery Monitoring Systems (BMS), which completely detect the risk of “hidden failures” that are often missed by ordinary UPS self-test cycles by monitoring SOC and ohmic values in real time.

Meticulous Visual Inspection

Although it may not sound technical, physical inspection is indeed the first critical step in figuring out the condition of UPS batteries. In the eyes of senior facility managers, this is actually identifying the physical manifestations of chemical stress:

• Shell bulging and deformation: This is usually caused by thermal runaway or overcharging. Once the battery case bulges, it means that the internal pressure has destroyed the structural integrity, and the battery is basically a ticking time bomb.
• Terminal corrosion: White or colored crystals growing on the terminal will increase the contact resistance, resulting in excessive heat during discharge.
• Electrolyte leakage: Even a little leakage near the pole or sealing ring may cause a ground fault, which clearly marks the end of the battery’s service life.

Internal Resistance (IR) Measurement

Voltage readings are often only “surface” data, and the voltage may appear to be stable until the battery is almost completely dead. To truly assess state of health (SOH), we must measure internal resistance.

In VRLA (valve-regulated sealed lead-acid battery), the internal resistance will gradually increase as the battery ages, the plates are sulfated or the electrolyte dries up.

• 20-25% rule: If the measured value is 20% to 25% higher than the initial reference value (the internal resistance of the battery when it was first put into production), this is the most reliable early warning signal.
• Discharge capability: High internal resistance will limit the ability of the battery to output high current. UPS needs high-rate discharge capability at the moment of power switching. If the internal resistance is too high, the battery will not be able to supply it.

Controlled Discharge And Load Test

The third level of checking UPS battery condition is a load test. This is the only means of verifying whether the battery can really achieve its nominal performance.

• Simulated power outage: By applying a controlled load that simulates the actual power consumption of the data center, we can measure the rate of voltage drop over time.
• Capacity verification: If the battery cannot maintain the required voltage within the time of rated capacity (for example, it cannot hold at 80% of the expected operating time), then it is considered “end of life” and must be replaced, otherwise it may cause downtime at any time.

Transitioning To Automated Battery Monitoring Systems

The kind of manual “snapshot” inspection once or twice a year actually has a huge vacuum in safety protection. In a high-availability environment like the one served by Gerchamp, these “hidden failures” are likely to erupt between inspections.

The current industry trend is a full shift to automated Battery Monitoring Systems (BMS). Unlike the standard UPS self-test cycle, a professional BMS can provide:

• Real-time data: Continuously monitor SOC (State of Charge), float current, and ohmic value (internal resistance/conductance).
• Precision temperature tracking: Monitoring the negative terminal temperature and ambient temperature to detect early signs of thermal runaway.
• Trend analysis: The decay trend of the battery can be identified weeks or even months before it fails.
• Reduce risk: Avoid the operational errors and safety risks of manual probe testing on charged high-voltage battery strings.

By integrating a specialized Battery Monitoring System, data center managers are able to move from “firefighting” maintenance to a “predictive” model. In this way, checking the status of a UPS battery is no longer a regular headache, but a precise task automatically completed by the system 24/7/365.

Author: Kevin

I am a Senior Engineer at Gerchamp’s BMS R&D Department with over 12 years of industry experience. I specialize in leading the architecture design and core algorithm development for our advanced Battery Management Systems.