Short answer: A lithium-ion cell discharges over a far wider temperature range than it charges over. Battery University's table gives Li-ion a discharge window of -20°C to 60°C and a charge window of 0°C to 45°C, and Google's Pixel 8 safety guide is blunter still: "Do not use or charge the phone at ambient temperatures lower than 0°C (32°F) or higher than 35°C (95°F)." So the first thing an unheated garage, shed, porch or lock-up takes from a phone camera is not the picture. It is the ability to put back the power the phone is spending. The visible failure is a device that is plugged in and going flat anyway, then a shutdown with no warning. And the case where the phone does accept a charge while it is that cold is the worse outcome, not the better one.
I build Background Camera RemoteStream (disclosure: I wrote it), so a fair amount of my mail is people describing where they put a phone, and a recurring answer is a place with no heating in it: a detached garage, a shed, a carport, an unheated porch, a lock-up. In August nobody asks about it. In February the same setup produces a mail that reads like a fault report and is not one.
I have written before about the heat side of this, which is the side everybody covers, because it is the side that shows up during testing on a warm afternoon. The cold side is nearly undocumented in the phone-as-camera genre, and it fails in a shape that does not look like temperature at all.
The two windows are not the same window
This is the whole article in one idea, and it comes straight out of the battery literature rather than out of anything Android does.
Battery University's BU-410 gives permissible temperature limits per chemistry. For lithium-ion the discharge range is -20°C to 60°C (-4°F to 140°F); the charge range is 0°C to 45°C (32°F to 113°F). The charge advisory column for that row opens flatly:
"No charge permitted below freezing."
The article states the general principle plainly:
"Batteries can be discharged over a large temperature range, but the charge temperature is limited."
And freezing is not the only line. The same page puts the fast-charge window higher than most people assume:
"Li-ion can be fast charged from 5°C to 45°C (41 to 113°F). Below 5°C, the charge current should be reduced, and no charging is permitted at freezing temperatures because of the reduced diffusion rates on the anode."
So there is a derating band above freezing before there is a prohibition at it. A shed sitting at 3°C is already outside the fast-charge window while the thermometer still reads above zero, which is part of why the first symptoms arrive on nights that do not feel cold enough to explain them.
Read that against what a 24/7 camera actually does. It is a device permanently discharging and permanently charging at the same time, in whatever the room does. Take the room toward freezing and only one of those two activities is still inside its rated window.
That asymmetry is why the failure does not look like cold. A midwinter shed does not produce a phone that will not record. It produces a phone that records perfectly and cannot replace what it spends.
What the handset maker says about the handset
The battery literature is generic. The device documentation is not, and Google is unusually direct for a consumer safety page. From the Pixel 8 safety and regulatory guide:
"Your phone works best in ambient temperatures between 0° and 35°C (32° and 95°F), and should be stored between ambient temperatures of -20° and 45°C (-4° and 113°F)."
And, separately, under operating temperature:
"Do not use or charge the phone at ambient temperatures lower than 0°C (32°F) or higher than 35°C (95°F)."
Two things worth noticing.
First, the storage floor is -20°C and the operating floor is 0°C. That gap is exactly the gap between the phone survives this and the phone should be working in this. A phone camera lives permanently in the second category. It is not stored in the shed; it is on duty in the shed.
Second, the sentence bans use at the same threshold it bans charging -- a stricter line than the chemistry alone requires, since BU-410 puts lithium discharge down at -20°C. A handset is not a bare cell. It is a cell plus a charge controller plus a fuel gauge that was calibrated somewhere warmer.
The failure mode, in the order you will actually meet it
Here is the sequence, and it is worth knowing because the first three steps look like a software fault.
- The room drops. Nothing happens. Recording continues. This is the discharge window doing its job and it is why the problem is invisible for the first cold snap or two.
- The battery percentage starts falling while the cable is in. This is the moment people write to me, and it is almost always reported as a charging fault or a cable fault. The charge controller has stopped accepting current, or is accepting so little that it cannot keep up with what a camera workload draws. BU-410: "The internal resistance of all batteries rises when cold, prolonging charge times noticeably."
- The phone shuts down without warning. Google's own temperature-state page states the outcome directly: "If your phone's temperature is below 0°C / 32°F, it may shut down suddenly."
- You find it dark, warm it up, and it works. Which reads as a false alarm and is not one -- see the next section.
The uncomfortable part is step 4. A device that recovers when you bring it in teaches you the wrong lesson: nothing about the recovery tells you whether step 2 did lasting harm, and you cannot tell by looking.
The part that does not come back
This is the one I would not have believed without reading it, and it is the reason the cold side is worth an article rather than a footnote.
The dangerous case is not the phone refusing to charge. It is the phone appearing to charge:
"Many battery users are unaware that consumer-grade lithium-ion batteries cannot be charged below 0°C (32°F). Although the pack appears to be charging normally, plating of metallic lithium occurs on the anode during a sub-freezing charge that leads to a permanent degradation in performance and safety. Batteries with lithium plating are more vulnerable to failure if exposed to vibration or other stressful conditions."
Three consequences for anyone running a phone as a fixture.
It charged fine is not evidence. Per that paragraph, a healthy sub-freezing charge and a damaging one produce the same observable behaviour. A percentage climbing on a lock screen is not a measurement of whether the cell is being harmed.
A protective refusal is the good outcome. If the charge controller cuts off and the battery sits there falling, that is the device declining to hurt itself. It reads as a defect and is closer to a safety feature. The failure you want to avoid is the permissive one.
The damage is stored, and the mounting spot collects on it. That last sentence is the one that matters for a fixture rather than a pocket phone: plated cells are "more vulnerable to failure if exposed to vibration or other stressful conditions." A phone camera is rarely sitting still on a desk. It is on a roll-up garage door, a shed wall that bangs, a carport post, a gate. The place that made the sub-freezing charge possible is very often the same place that supplies the vibration -- and the cold night that plated the anode and the morning the cell finally fails can be months apart, which is exactly why nobody connects them.
BU-410 is also explicit that cold charging is possible, just not at any current you would recognise as charging: the allowable rate at -30°C is quoted as 0.02C, which the article says would "stretch to over 50 hours". That is a laboratory footnote, not a workaround.
Android has a Cold state, and the door to it is labelled with the opposite problem
Here is the detail that made me want to write this up.
Recent Pixels ship a device temperature diagnostic with four states: Cold, Normal, Warm, Elevated. Cold is a first-class state with its own text and its own tip. Google describes it:
"The cold temperature state indicates that your estimated device temperature is lower than normal. Your phone may be cold if it was exposed to cold outside temperatures or close to an air conditioner vent."
And the accompanying tip:
"Make sure to let your phone warm up gradually."
Now the part that matters if you want to find that screen. The documented path is Settings, then Battery, then Battery diagnostics, then a row called Phone is very warm. The only doorway into the cold diagnosis is a menu item named after being hot. The page also flags the feature as "Available on Pixel 6a and later", so on an older donor handset -- exactly the kind of phone this genre is built around -- the screen is not there at all.
It is a UI-naming observation, not a bug, and I have no evidence anyone was confused by it. But it is a fair summary of the state of the art: the platform models cold, and almost nothing written about repurposed phones is looking for it.
Warming it back up is its own event
The tip above is doing more work than it looks like.
Air holds less water when it is cold. Move a phone that has been sitting at freezing into a heated room and the room's moisture condenses on -- and, more to the point, inside -- the coldest object present, which is the phone. That is a different failure from the charging one, it is mechanical rather than electrical, and it happens during the recovery, not during the cold.
Google's guidance is to let it warm gradually, and the safety guide's general instruction for a device outside its range is in the same spirit:
"Move the device to a cooler (or warmer) location and wait a few minutes before attempting to use it again."
Neither source gives a rate, a duration or a humidity threshold, and I am not going to invent one. What I do is bring a cold phone indoors inside a closed bag and leave it shut until the bag is at room temperature, so the water condenses on the bag rather than the phone. That is a common photography habit, not a documented Google recommendation, and I flag it as such.
What I would actually do about it
Ranked by how much they buy you for the effort, and none of them require buying anything.
- Put the phone on the warm side of the glass, not the cold side. A phone indoors looking out through a window is in a heated room; a phone in the shed looking at the same lane is not. That one decision moves the entire problem, and the only thing it spends is the angle.
- If it must live in the cold space, put it on an interior wall, away from the door and the roof. A detached garage's interior wall shares heat with the house. Its roll-up door does not.
- Prefer a mount that does not shake. Given the vibration finding above, the wall beside the roll-up door is a better bracket than the door itself, and it costs nothing to choose at install time.
- Treat the cold snap as the test, not the install day. A setup validated in October tells you nothing about January. One number to watch: the battery percentage over a cold night with the cable in. Flat or climbing is fine. Falling means the charge controller has stepped back.
- Do not insulate a phone that is also charging. Wrapping or boxing it is the exact move the heat article warns against, and a camera workload plus a sealed enclosure lands you on the other end of the same range. Enclose the space, not the device.
- Accept the seasonal answer. For a genuinely unheated space in a genuinely cold climate, a phone is the wrong fixture for December and a fine one for the other nine months. No software fixes a rated operating floor.
What I cannot tell you
Some honest unknowns, stated plainly, because a guess here would be worse than a gap.
- Where your specific handset actually cuts off. The 0°C figure is Google's guidance for Pixel and BU-410's for the chemistry. What a given charge controller does at, say, 3°C is a per-device decision I have not measured and have not seen published for the used handsets people actually mount.
- Whether it resumes on its own, and whether anything tells you it happened. I have not tested enough handsets to say.
- How much a single cold charge costs you. The literature says the harm is real and cumulative. It does not give a per-event number, and anybody quoting you one should be asked where it came from.
- How much vibration is enough to cash in that damage. BU-410 names vibration as an aggravating factor; it does not quantify it, and neither will I.
- Whether Pixel's estimated device temperature tracks the cell closely at the cold end. The page is explicit that it is an estimate, and that Pixels normally run above ambient because of internal heat. Both cut the wrong way for a cold reading and I do not know by how much.
The short version
The heat problem is a load problem and you can engineer around it: less work, more air. The cold problem is a charge acceptance problem and you mostly cannot -- you can only move the phone, or accept the season. The tell is a phone that is plugged in and going flat anyway. But the reason to act on that tell is not the night you notice it: a sub-freezing charge banks its damage silently, and a bracket that shakes is where the bill eventually comes due.
If you have run a phone through a winter in an unheated space, I would like to hear what it actually did: which handset, roughly what temperature, and whether the battery held, fell, or stopped and started. That is the data nobody in this niche seems to have, including me.
App: Background Camera RemoteStream on Google Play - more at https://superfunicular.com
Sources: BU-410: Charging at High and Low Temperatures - Check & understand your Pixel's temperature - Safety and regulatory guide for Pixel 8 and Pixel 8 Pro
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