iPhones have an internal thermometer which monitors the temperature of the battery - it’s how the deice knows that it’s either too hot or too cold to function.

Clearly, as a monitor for the internal temperature, it’s not measuring the external, ambient temperature. But I wanted to know how much effect the ambient temperature would have.

As such, I tested decided to run some tests to see with a device, some cold temperatures and a digital thermometer.

The Details

The Files
The temperature of the battery is recorded in either knowledgeC or within a biome:

• /private/var/mobile/Library/CoreDuet/Knowledge/knowledgeC.db
• /private/var/mobile/Library/Biome/streams/restricted/_DKEvent.Dasd.Batterytemperature

In knowledgeC.db, search for ZSTREAMNAME '/dasd/batterytemperature'.

In both files, the value is recorded in celcius, but requires dividing by 100.

So a value may show 2800, in which case 2800 / 100 = 28c.

Note that the point of the test was purely to see how the internal temperature fluctuations matched the fluctuations recorded by the digital thermometer.

Test Scenario 1
An iPhone X without case, and running iOS15.2.1, was placed inside a freezer alongside a digital thermometer for 15 minutes to assess how the Battery Temperature was affected.

At one-minute intervals, the freezer was opened and the temperature shown on the thermometer was documented.

After 15 minutes, the devices were both removed and monitored as their temperature rose for a further 10 minutes.

Orange dots/lines = iPhone | Blue dots/lines = digital thermometer.

Test 1 Conclusion
The recorded temperatures in knowledgeC.db were fairly sporadic, with no real discernable cadence. However, as can be seen in the graph above, the readings were in line with the readings of the digital thermometer.

Test Scenario 2
An iPhone X without case, and running iOS15.2.1, was placed outside in -5c/23f temperatures and left untouched for 15 minutes, brought inside for 10 minutes and then returned outside for another 15 minutes before being brought inside again.

This test was intended to provide more real-world testing conditions of moving from outdoors to indoors with a view to monitoring temperature accuracy and the reactivity of the monitoring.

Orange dots/lines = iPhone | Blue dots/lines = digital thermometer.

Test 2 Conclusion
As with Test 1, the recorded temperatures in knowledgeC.db were fairly sporadic, with no obvious cadence. However, also as seen in Test 1, the readings were in line with the readings of the digital thermometer.

Wrapping Up

In a locked state, with little activity occurring on the device, the battery temperature is heavily affected by the ambient temperature of the environment, matching the pattern of the fall and rise of the thermometer temperature.

The cadence of the records is sporadic with no obvious reason or pattern.

As can be attested by anyone who uses their phone for prolonged periods of time, usage of the device will result in increased internal temperature. So device usage needs to be considered if looking at using this artifact as evidence.