Thirty-five percent, and almost never the rating

In the TÜV Baurechtsreport 2026, 35 % of backup power systems in special buildings show significant defects — hospitals, schools, high-rise buildings, shopping centres. The figure comes from the TÜV association's release, reported by the Bauletter services on 4 September 2026.

What stands out is not the rate but the three examples given: a generator that will not start; fuel that is too old; a failed storage battery. Not a sizing error, not an overload, not a design fault. Three things that fail while the system is idle.

A failure does not announce itself with a reading

Fuel ages by calendar, not by operating hours. Fill the tank before the season and leave the set standing, and you have diesel in a tank whose condition nobody knows. Water settles, ignition quality drops, and the filter turns an old problem into a new one.

A storage battery discharges on its own, even with nothing connected. It does not hold its charge indefinitely, and it does not warn you in advance.

And a generator that has not run for months is not a tested machine — it is an unknown one. The difference between "it is there" and "it starts" only appears during a start attempt, and that attempt happens in the inspection, not in the emergency.

An inspection is not a load run

A start attempt with nothing connected proves very little. That the engine runs says nothing about whether the output carries the load, whether voltage holds under load, and whether fuel supply lasts in continuous operation. A load run is a different test from a glance at the tank.

In a rental fleet there is a second factor: the location. A unit in the yard is seen regularly; a unit standing at a customer site is seen when it is needed. The test interval keeps running either way.

The report names no culprits, and it does not need to. All three causes are maintenance topics — and maintenance is the discipline that gets postponed first in day-to-day business.

What belongs on the inspection sheet

  • Date of the last load run, not the last visual check.
  • Condition and age of the fuel, not just the level.
  • Starter battery: voltage and year of installation, not the word "present".
  • Who inspected it — one line that actually counts in an emergency.

A battery does not replace maintenance, it moves it

Put a battery unit where the generator stood and you trade fuel and a starter motor for state of charge and cell monitoring. A state of charge can be read without the unit having to start; a tank level says nothing about whether it will start. That is the real gain — not the kilowatt figure on the datasheet.

What remains is the question of the load path. Whether the protective device downstream still matches the source is covered in a separate article: What the RCD sees when the source changes.

So the question for the next site walk is not "is the system there", but "when did it last run under load — and is that written down anywhere".

Source: TÜV-Verband fordert Offensive für krisenfeste Infrastruktur — Bauletter/BAULINKS, 4 September 2026.