Originally Posted by
missydarlin
But do we even know at this point that it was the battery or the sleds that was smoking? While the thread title mentions the battery specifically, all we know for sure (unless I missed something) is that the device overheated and smoke emanated from some part of the iPhone/card reader dock.
There's nothing else in there that can ignite or offgas like that.
The two options are the primary battery in the device or the booster battery in the sled. No other component failure could cause that scale of issue. If an electrolytic capacitor vented, about the worst that could happen is that the device would stop working and if you were *right there* you might smell "hot electronics". The other factor is "circuit protection" - because shorting a lithium ion battery (causing it to discharge rapidly) is such an issue (fire, nasty fumes, death and property damage), various circuits in the devices will monitor power flow, and if the safe limit is exceeded for even a moment, the device power is shut down.
The batteries have protection in them too. They are the last line of defense in a battery failure. My suspicion is that a failure condition caused this primary circuit protection to go off and vent the fumes. Totally worked as designed.
The problem is that two interconnected failures can happen simultaneously. The edge between "managed failure" and "catastrophe" is razor thin.
The device manufacturers with big consumer businesses are extremely aware of these risks and do amazing engineering to prevent them - if 1 out of 25,000,000 iPhones had catastrophic early-life battery failures, the new 6s/6+s could have already killed or severely burnt someone - they have a lot at stake here. The sled people, bright as they are, are not battery pack design experts selling tens of millions of them into the global marketplace and they will always be riskier.
When Lithium was the hot new thing in battery packs for laptops in 1994, I was in an lab space at a major computer company when a pack cooked off. It burned through a 1.5" thick tabletop in an astonishingly short period of time and ABC, CO2 and Halon extinguishers were useless. I have been less fearful for my life in earthquakes, hurricanes and Black Friday sales. The battery in a modern phone is roughly about a quarter the energy as one would find in a a laptop that set a Formica-covered table ablaze.