UPS Uninterruptible Power Supply Principle and Lead-acid Battery Maintenance（part 2)

III. Routine Maintenance of Lead-Acid Batteries: Follow These 5 Tips to Extend Battery Life by Two Years

1. Temperature control – the number one killer of battery life

The optimal temperature for lead-acid batteries is 20-25℃. For every 10℃ increase, their lifespan is reduced by approximately half. In summer, when the temperature in the computer room exceeds 30℃, the rate of corrosion and water loss in the battery’s float charging state accelerates significantly.

2. Float charge voltage – neither too high nor too low.

Float charging refers to the UPS continuously supplying a sustaining voltage to the battery after it is fully charged. For a single 12V battery, the float charge voltage should be stable at 13.5-13.8V (at 25℃).

Excessive voltage leads to water loss, thermal runaway, and battery swelling.

Low voltage leads to incomplete charging over time, plate sulfation, and irreversible capacity loss.
Temperature compensation function: automatically reduces float charging voltage in hot weather and automatically increases it in cold weather. For example, some industrial models from Ubis Power Supply have this compensation circuit built-in.

3. Regular charge and discharge cycles – don’t let the battery “sleep.”

If a battery is kept in a float charging state for a long time (without interruption of power), the active material on the plates will become passivated, and its capacity will gradually “starve”.

4. Cleaning and tightening – small details, big problems

Dust and moisture can cause terminal creep or poor contact. Vibration may loosen connecting bolts, generating sparks or overheating.
Replace immediately.

5. Record replacement cycles – Don’t be misled by claims of “maintenance-free”.

The term “maintenance-free” simply means no electrolyte needs to be added, not that it won’t break. Ordinary lead-acid batteries are designed for a lifespan of 3-5 years, but in actual use, after more than 4 years, their capacity may be less than 50%.
The discharge time method: record the backup time when the battery is new, compare it annually, and prepare to replace it when it drops below 70%.

IV. Intelligent Battery Management of UPS: Why are some brands more worry-free?

The maintenance points mentioned above are, frankly, difficult to maintain consistently by relying entirely on manual labor. Therefore, most professional UPS systems now incorporate intelligent battery management.
UPS (a manufacturer specializing in customized industrial and medical UPS systems), which I’ve worked with, has several practical designs in this regard:

Three-stage intelligent charging: constant current → constant voltage → float charging, to prevent overcharging.

Automatic battery self-test: It can be set to automatically perform a discharge test once a week or once a month and generate a report.

External temperature sensor: The probe is attached to the surface of the battery, and the UPS automatically adjusts the float charge voltage.

These functions aren’t some kind of mystical technique; they simply automate the aforementioned maintenance steps. For scenarios like hospitals and factories where there isn’t someone specifically monitoring the batteries every day, this can indeed save a lot of trouble.

V. Conclusion: Buying a UPS is not the end of the process.

Many people spend a lot of money on UPS systems, then leave them in a corner and never look after them again, only to find the batteries are already dead when a power outage occurs. A UPS main unit typically lasts ten years, but the batteries must be replaced every three to five years. Understanding the principles and characteristics of lead-acid batteries, and regularly performing a few simple tasks—temperature control, voltage regulation, discharging, cleaning, and recording—will ensure your backup power supply truly “steps in” in critical moments.

Finally, let me be frank: if your organization has multiple critical loads, instead of getting hung up on the UPS brand, you should first establish a battery maintenance system. Even the best UPS is useless with a bunch of aging batteries.