I have been investigating this problem for a while now (still doing) and here is some information that could be useful:
Many ppl complain that their iPhone6 and 6S dies very fast when temperature pass the 0-line.
It is not easy to explain the whole truth because there are alot of parameters that is included why this happens.
One of the parameters that I wanted to investigate is how the amount of charge-cycles make the battery more vunerable to cold. To do this I contacted Apple support and explained my questions.
After 30 min we hang up and I was told that there is no "recommended amount" of charging cycles before the battery if finnished (more or less). In one way I can understand why they do not publish this information because mobile phones are affected of somany different kind of situations and environments.
But still, most other products have a Maximum Charge Count limit, so I would be very amazed if Apple didnt have this information. They just dont want ppl to know (maybe for a insurance reason).
There is alot of speculation regarding what the iPhone battery MCC is, but Im not intrested in speculations. I want proof.
Another very intresting parameter is the capacity of the battery.
For exampel an iPhone6 battery have 1810mAh.
But that is in a specific temperature.
If you measure the capacity in +25 degrees and -5 degrees you will get 2 very different values.
I asked Apple in what temperature they measure the battery but they didnt know, and asked me to go talk to
some Apple Service Store about it. So I did.
But the answer I got from them is not what I expected.
They said that the capacity is the same in all temperatures.
But this can not be right because of this:
When the temperature go down the battery resistance go up.
And if you have some basic knowledge in electronics you know what happens when the resistance go up (Ohms Law).
The result will be that the Ampere or Voltage will go down = the capacity willbe less.
There is a very nice site where you can read everything about batteries: Batteryuniversity.com
So, my conclution regarding capacity in different temperatures is that Apple is wrong and Im right.
Another thing that I talk to Apple about was ppl who claim that their mobile phone battery is bad.
He told me that more than 95% of the mobile phone batteries that they test is accually good, and they return the
phone to the customer again.
At that point I had not started my testing yet so I could not say anything about that information.
But now, after testing both new and old iPhone 6 and 6S I can say: He was wrong about this as well.
I use a program named coconutbattery (strange name) to get the information from the battery.
Here you see everything in real-time.
Charge cycles, capacity when the battery was new, current capacity, manufacture date etc.
With this program I have been (and still doing) made some documentation about how the battery capacity
behaves in different temperatures.
The result is maybe not so cheerful for most iPhone6 and 6S owners but it shows this:
When the battery is new and the temperature drops down to -10 degrees the battery capacity go down with around 25% (-+5%). And this is for brand new iPhone6 with charge cycle count: 1
When the test starts Im at around 25-27 degrees (battery temp sensor).
The capacity remains 100% down to around 10 degrees.
Between 10 and 0 degrees the capacity go down about 5%.
Its below 0 things tharts to happen, or below -5 to be more specific.
Now, if you do the same test on used phones with a Cycle Count of 200-600 you will get this:
To start with the battery capacity (when fully charged) will be around 85-95%.
I begin the test at a temperature of 25-27 degrees C.
As with the new phones, not so much happens before you get to 10-12 degrees C. It remains at 85-95%.
Between 10 and 0 the capacity go down about twice as much as on a new phone.
The intresting is that when you get further down in temperature the battery on an old phone gets "instable".
It can jump down ALOT compared to a new battery.
In my testings at -10 degrees the capacity went down so much that It could easily explain why alot of used
iPhone6 phones die in cold temperatures.
Now, if you think about what Apple said regarding the batteries and that they send home 95% of their customers that complain about bad battery, its easy to understand how they test the battery.
They probably test the battery in room temperature, and sure, in room temperature your battery will be good (more or less). Its when the temperature climb below 0 they will see the "real" problem.
There is ofcourse ALOT more to talk about regarding iPhone batteries and cold climate but this might be a good start.
