Good or bad habits generally die hard, and this applies to all areas of daily life, including tech. In the world of smartphones, we hear or read the same advice repeated over and over again, but we no longer take the trouble to check its validity, even though the technologies they concern have evolved significantly over time.
Regarding batteries, we have been talking about the need to calibrate them since the beginnings of mobile telephony. But is it really useful? A detour through the history of the “portable” is essential.
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In their early days, phones were equipped with nickel batteries (nickel-cadmium more precisely, abbreviated to Ni-Cd). This technology suffers from a main disadvantage: the “memory effect”, which manifests itself by a progressive decline in the ability of a battery to deliver a sufficiently high voltage.
This loss of performance can occur when a nickel battery is partially discharged and then recharged repeatedly. During partial discharges, only part of the battery cells are used. The unused cells then begin to form cadmium microcrystals, which grow larger over time. These microcrystals increase the current resistance of these cells, which leads to a reduction in the electrical capacities of the battery, which now only bases its estimate on the capacity of the cells recently used. The battery thus “thinks” it has less capacity, and the autonomy of our devices decreases.
There is only one solution in this case: you must carry out a complete discharge (which allows the microcrystals to disappear), then recharge the battery fully so that it “regains awareness” of its real capacity.
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This phenomenon predates the advent of smartphones seems to have left its mark since today, many people think it is necessary to completely discharge the battery before recharging it. But today, lithium-ion batteries are omnipresent, even more and more frequently replaced by silicon-carbon models, as in the recent Oppo Find X8 Pro or the Magic 7 Pro from Honor. To find out if these models also require calibration, we called on Olivier Simon, battery expert at DXOMARK, to obtain some clarifications.
Is it still useful to calibrate smartphone batteries?
Our main question was the real usefulness of calibrating a smartphone’s battery, especially since today, the vast majority of terminals use lithium-ion batteries. These accumulators offer many advantages over nickel batteries, particularly in terms of energy density. Above all, as Olivier Simon confirms to us, they do not suffer from the memory effect and can be partially discharged as many times as desired without suffering any particular degradation.
But then, why do some smartphones, like Google Pixels, offer to charge the battery from 100% from time to time to calibrate it? According to Olivier Simon, it can indeed be interesting to do it from time to time (approximately every one to three months), but not for the same reasons as nickel batteries. Today, sometimes charging your smartphone up to 100% allows it to display the remaining percentage more precisely. Concretely, the percentage displayed on the mobile screen can “go wrong”, and it is above all a question of making this figure as faithful as possible to reality.
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Despite everything, the expert does not seem entirely convinced by this approach, because according to him, it only comes down to a handful of percent anyway. In addition, calibration has no impact on the real autonomy of smartphones.
It should first be noted that the 20%-80% rule is not a myth, which Olivier Simon confirms. This rule actually recommends not letting the charge level of your smartphone drop below 20% and not charging it beyond 80%.
Limit the charge of your smartphone
Why limit the load to 80%? Although Li-ion batteries offer very good performance, they are also very sensitive to extreme conditions. Lithium battery cells degrade quickly when left for too long or too high a charge, the former being the worst. Most smartphone manufacturers also offer a feature that limits the charge to a predefined level (generally between 70% and 90%). This is for example the case of Apple, which includes this function in its Optimized Charging option for iPhone, or of Google on its Pixels.
And for those who need the full capacity of their battery to face long days, fear not. For several years, phones have learned from your habits to stop charging at an intermediate level (usually around 80%), then finish it to show 100% when you need it. For example, most smartphones recognize your morning alarm and pause charging at 80%, only to resume charging to reach 100% just in time for you to wake up.
Avoid extreme temperatures
The second enemy of lithium batteries is temperature. On the one hand, heating batteries damages the cells in the long term, and the ideal is to keep them below 40°C. This is why it is better to avoid long charging sessions and, if possible, favor several small charges throughout the day. With the democratization of fast charging, this should be less and less restrictive, especially since there is currently no indication that fast charging damages batteries more quickly… provided once again that we avoid long sessions that heat up your terminal.
On the other hand, exposure to cold can also have a negative impact on battery health. In fact, manufacturers generally indicate that below 0°C, the performance of accumulators can be reduced. This applies to both discharging and recharging, which is not recommended in negative temperatures.
Under these conditions, metallic lithium crystals can form, leading to performance degradation and increasing the risk of failure. In practice, if you charge your smartphone in a very cold environment, the charging speed will be reduced to avoid damaging the battery.
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