(Motorsport-Total.com) – Only two years ago, Fernando Alonso completed the entire 2024 Formula 1 season with just one battery, and the control unit was only replaced at the last Grand Prix of the year in Abu Dhabi. An impressive statistic that highlighted the then reliability of the Mercedes power unit.
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Two years later, the situation looks very different. The failures in the cars of George Russell and Kimi Antonelli are an alarming signal, especially considering that the Mercedes customer teams McLaren and Williams also had problems in the first races of the year.
Already last season, it was emphasized with regard to the new rules for 2026 that optimizing temperature management would become a decisive factor. Also because in the new Formula the role of the battery is significantly more central than in the previous technical cycle, in which the hybrid share was much lower.
So far, Mercedes seems to have suffered under high temperatures and the operational load of the unit. Although some failures also occurred under cooler conditions, one must not forget that traffic on the track often played a role.
Therefore, not everything can be attributed solely to the outside temperature. The crucial point is that Mercedes apparently identified the cause and that the various defects go back to the same origin.
James Allison has already announced that with the introduction of the next batteries during the season, initial solutions should come. But what makes this year’s batteries so sensitive compared to the past?
Why Formula 1 needs different batteries than Formula E
The starting point is the charge and discharge cycle. Until last year, about 120 kilowatts (kW) were recovered during braking; today this value has almost tripled and is at 350 kW.
Although the maximum capacity of the battery has remained the same, i.e., only four megajoules (MJ), the load on the unit has increased significantly both in energy recovery and delivery.
This manifests in two ways: thermally, because more energy also generates more heat, and through micro-vibrations that add to the external vibrations. One of the reasons why the “Pit Boost” was introduced late in Formula E was precisely these vibrations, which led to losses.
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This topic is often underestimated because every battery has its own characteristics. The batteries used in Formula E, for example, would not be suitable for use in Formula 1. It’s not just about weight but also chemistry and development goals.
In a hybrid system like in Formula 1, the battery must operate with a very high C-rate, i.e., an extremely high ratio between power delivered or absorbed and the capacity of the pack.
At its core, Formula 1 needs a battery that can absorb and deliver large amounts of energy very quickly, with correspondingly fast charge and discharge cycles. In Formula E, on the other hand, the focus is on energy density: a pack that can store a lot of energy and is empty despite recuperation at the end of the race.
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Why cooling is such a big issue
Battery packs with very high C-rates generate a lot of heat in each cell, and dissipating this heat becomes a complex challenge that goes beyond just the outside temperature.
It is no coincidence that Mercedes stated that Russell’s battery in Montreal was severely damaged by the temperatures reached – before and after the vehicle was switched off – more than by chemical factors, so it had to be shipped back to England.
Problems can also arise with batteries at ambient temperature if they are not managed correctly, which is why the defect in Canada goes beyond the external “cold”.
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This is a crucial point because the temperatures must be distributed as evenly as possible across the entire battery pack. If even a few cells do not operate in the optimal range, the problem can cascade across the entire module.
Therefore, thermal control is approached on multiple levels, both on the software side – which is much more complex than it seems – and through special physical solutions.
Batteries from different manufacturers differ
An interesting aspect is that, as seen in the picture of the Mercedes battery pack from last year (below), internal coil pipes run through which a special liquid circulates to keep the temperatures in the ideal range.
Of course, the contribution of cool air also plays a role, but the liquid cooling system remains a central component for stabilizing the thermal behavior of the battery. However, it is obvious that the problems cannot be reduced solely to the amount of cooling air supplied, especially since they have occurred in various teams.
The chemical composition of the battery can also play a role, varying from manufacturer to manufacturer to find the most efficient solution. Different approaches can prove to be more sensitive both in terms of power density and thermal stability.
Although they are all lithium-ion batteries, there is some design flexibility in certain areas that can lead to significant differences. Mercedes has already stated that it has identified the cause and that the problem should be solved with the upcoming batteries.
But in 2026, it is not surprising that this topic has become significantly more complex than in the past – even for a manufacturer who counted reliability among its strengths in the previous technical cycle.