The Shanghai Consumer Council, a watchdog group in China, reported last week that eight iPhone 6 devices had spontaneously combusted. Apple’s response is that “external factors” were to blame for these “thermal events” with the phone batteries, the BBC reported Wednesday.

Batteries have been causing headaches for smartphone manufacturers over the past year.
Apple recalled iPhone 6 and 6S models in China after they switched themselves off before the battery was depleted, while Samsung was forced to recall millions of Galaxy Note 7 devices due to their tendency to overheat and catch fire .

Samsung Tendency to over heat and catch fire

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Samsung is having some trouble identifying what went wrong with the Galaxy Note 7, which earlier this year was recalled due to a high number of battery explosions , but someone else believes they have the answer.

Manufacturing engineering company Instrumental has performed a teardown of the device , and found that the battery simply did not have enough physical room for error.

The problem had more than one factor, the teardown found. A phone battery is made up of positive and negative layers, with separators to keep them from touching and sparking. In order to streamline the size of the battery and maximise space, these separators may have been too thin. Moreover, Samsung made the battery thinner, removing thickness margins.

When batteries are charged, they swell a little. Around 10 percent extra space is required, but the battery entirely filled its 5.2-millimetre-deep pocket, with very little space around the edges. Add the normal pressures of day-to-day handling, and the risk of explosion goes up.

“Looking at the design, Samsung engineers were clearly trying to balance the risk of a super-aggressive manufacturing process to maximize capacity, while attempting to protect it internally,” the teardown reads. “Samsung took a deliberate step toward danger, and their existing test infrastructure and design validation process failed them.”