British researchers have published an article showing that charging by induction generates more heat and therefore damages the battery of a smartphone. An observation that we have sought to reproduce, revealing some nuances.
A few days ago, researchers from the University of Warwick in the United Kingdom published the results of their studies on wireless inductive charging of smartphones. Using a thermal camera, the study authors took readings while charging an iPhone 8 Plus. They compared the results obtained with the official wired charger of the iPhone with those of a wireless induction charger. For their experiment, the researchers chose a Mophie Wireless Charging Base charger, which we tested elsewhere.Mophie Wireless charging base Rating TechnologiesTips Give your opinion read the test
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In the publication of the researchers, several conclusions are drawn. First, inductive charging heats up the smartphone more than wired charging. When charging with the original charger, the temperatures noted by the authors do not exceed 27°C. On the other hand, this maximum temperature increases to 33°C during their induction charging test. The researchers go even further and demonstrate that poor positioning of the smartphone on the charger leads to an even greater temperature rise. To compensate for the offset of the coils in the charger and the smartphone, the charger is forced to increase its power.
Effect of ambient temperature on the life cycle of Li-ion batteries. © Journal of Power Sources
Also in this British study, we can find the graph that we reproduce above. It relates the temperature reached by the battery and the number of charge cycles it can withstand, or, in a way, its lifespan. It can be seen that a temperature difference of 3°C reduces the maximum number of cycles of the battery from 1 to 250, a reduction of 750%. This clearly raises the question of the relevance of wireless charging at a time when the lifespan of our smartphones always seems shorter.
Not all wireless chargers are created equal
Upon reading this study, we were surprised to see that it had only been carried out with a single model of induction charger. The Mophie Wireless Charging Base is one of the accessories recommended by Apple. Sold all the same 45 € on the site of the brand with the apple, it had collected only 3 stars during its passage in test in our laboratories. We wanted to partly reproduce the experiment presented by the researchers, by carrying out our own measurements.
To do this, we chose to carry out a charging test with an iPhone 8 with the wired charger supplied in the box, as well as with 3 induction models. Among these models are a Samsung EP-PN920 charger, a Google Pixel Stand and the famous Mophie charger used by the researchers. We have taken a series of temperature readings using our thermal camera, which you can find below.
As you can see, the wired charger is the one that causes the temperature of the iPhone to rise the least, while being the fastest. The Mophie charger used by the researchers is both the one that heats the smartphone the most and the slowest to recharge it. With the wired charger, we note a maximum temperature of 31,4 ° C, reached after 30 min. For the Mophie charger, we note a maximum value of 36,3°C. A difference of almost 5°C, not negligible if we refer to the graph presented above. With maximum temperatures of 32,1°C and 33,4°C respectively, Google and Samsung wireless chargers are less harmful to battery life.Google Pixel Stand Share your opinion
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What partly explains these temperature differences is the very design of induction chargers. While the Mophie model is just a rather thin wafer, the Samsung pad has grids for heat dissipation. A dissipation that also seems best achieved with a stand-type charger, like Google's.
The very principle of inductive charging tends to produce more heat, and therefore to degrade the state of smartphone batteries more quickly. However, not all chargers are equal on this issue and it is better to favor a model capable of dissipating heat properly. In our comprehensive tests, the Anker PowerWave 7.5 Pad Charger was the only one that received the maximum rating.Anker PowerWave 7.5 Pad Introductory price €50
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