26 hours of backup power: the myth of daisy-chained batteries

Daisy-chained batteries fail in a blackout: what a real simulation revealed

The theory that connecting several portable batteries in a daisy chain multiplies your backup time during a blackout has run into reality. An exhaustive home simulation, testing everything from lighting to using a phone as a modem, produced a crushing result: the chained setup did not work and lasted barely 26 hours. Practice disproves the logic of simply adding capacities together.

Those living in flats without a sunny terrace have it even tougher. The only viable recharging option is a low-power flexible panel, insufficient even in the sunniest months. The simulation showed that chaining batteries, far from adding up, penalises performance. Alternatives such as using the batteries independently offer a little more leeway, but dependence on the grid remains total.

The experience of a real blackout in April 2025 adds fuel to the fire. During those hours without power, numerous petrol stations could not sell fuel: their tanks were full, but they had no generator to run the pumps. Only Mercadona, according to testimonies, kept serving customers. That a critical piece of infrastructure like a petrol station lacks a simple generator says a lot about how fragile the system is.

The conclusion of the simulation is clear: anyone who wants to survive an outage longer than a day needs more than a handful of batteries. The combination of solar panels, a high-capacity battery and, for the most forward-thinking, gas bottles or a petrol generator remains the only reliable recipe. But in an urban flat, with no terrace or space, the options shrink to little more than torches and a power bank.

It is not alarmism, it is maths: with a maximum of 26 hours of backup power in the best setup, any blackout lasting longer leaves the family in the dark. And if the communications network goes down too, the phone as a modem becomes another battery drain. The question left hanging is how long it will take the next system failure to teach us what we refused to learn.