Backup Batteries Behind Mystery Minute-by-Minute Power Grid Dips
German researchers traced a once-a-minute frequency dip seen on power grids worldwide to synchronized self-checks by backup batteries in data centers.
For years, power grid operators on several continents saw the same puzzling pattern: a slight drop in grid frequency at the start of nearly every minute, appearing at the same moment in places as far apart as Europe, the United States, Australia and Malaysia. A team of German researchers now says it has found the cause. The culprit is not a faulty power plant but millions of battery systems, many of them in data centers, that check themselves on an internet-synchronized clock.
The study, led by researchers at Forschungszentrum Jülich, one of Germany’s largest national research centers, was published in the journal Nature Energy. TechCrunch reported on the findings Sunday, and the German science outlet wissenschaft.de covered the paper earlier this month.
What the researchers found
Every alternating-current power grid runs at a target frequency, 50 hertz in Europe and 60 hertz in North America, and operators work to keep it within a narrow band. Large swings can trigger blackouts, and persistent sags can wear out equipment, particularly hydropower turbines.
The team, whose senior author is Dirk Witthaut, a physicist at Forschungszentrum Jülich and the University of Cologne, found that the frequency on many grids reliably dips by a few millihertz once every 60 seconds. According to an earlier preprint version of the research posted on arXiv, the pattern showed up on the transmission grids of continental Europe, Great Britain and the Nordic countries, and in local measurements from the eastern and western United States, Australia, Iceland, South Korea and Malaysia. Wissenschaft.de said the published paper also cites South Africa.
The problem was brought to the researchers by TenneT Germany, the country’s largest transmission system operator, TechCrunch reported. The investigation took years. The team first looked at hydropower plants, which historically have been a major source of slow grid oscillations, but a model of a Scandinavian hydro control system could not explain why the minute-long rhythm was so steady. That pointed instead to something governed by a clock, Witthaut told wissenschaft.de.
Tracing the pulse to backup batteries
To test the idea, the researchers installed more than 80 smart power-quality meters across the Jülich campus, which has its own distribution lines, solar panels, a high-performance computer and large battery-based uninterruptible power supplies, known as UPS units. These are the battery banks that keep servers and other sensitive equipment running through short outages. The transformer feeding one of those battery systems showed a spike at the start of every minute.
The explanation, the researchers say, is that many UPS units and grid-scale batteries run a short state-of-charge check or self-test about once a minute, drawing a little power for a few seconds. Because the devices are connected to the internet, their clocks are almost perfectly synchronized. Manufacturers also appear to have independently chosen the same interval and to start the check at the top of the minute, wissenschaft.de reported. Each test is negligible on its own, but thousands happening at once produce a dip visible across an entire grid.
The preprint also showed the effect in an unexpected place: the island of Mallorca had no such pattern in 2019 but clearly showed one in 2025, after large battery storage was installed there.
Why it matters
The dips are small today, but they are growing as data centers and battery storage spread. Ireland offers the starkest example. Data centers accounted for 18% of the load on the Irish grid by 2022, according to TechCrunch, and between 2016 and 2021 the size of the minute-by-minute frequency drop there quadrupled, from 3 millihertz to 12 millihertz. Some recent dips have topped 20 millihertz. Ireland’s grid is built to tolerate swings of 200 millihertz, but its operator prefers to stay within 100, leaving less margin when the pulses coincide with other disturbances.
The researchers have cautioned that the link with data center growth does not prove every added fluctuation comes from data centers. In Scandinavia, operators have already tightened controls because the oscillations caused extra wear on hydropower turbines, wissenschaft.de reported.
What comes next
The proposed fix is simple: manufacturers should randomize when their devices run the checks instead of starting them all on the minute. In many cases that can be done with a firmware update. At least one UPS maker has responded since the team alerted it to the issue, according to wissenschaft.de, and the preprint noted that one manufacturer already shifts the timing daily.
The harder part may be getting everyone to act. The team detected similar periodic patterns from internet-connected household devices, including a smart oven and clusters of Raspberry Pi mini-computers, and Witthaut has said batteries may be only part of the problem. TechCrunch noted that a separate study found fewer than 3% of such devices run the latest firmware, and that because regulators can only act within their own borders, a global fix will likely require international coordination.
