Tom's Tech Corner: The Cold Truth About Warm Batteries
Dear Tom,
I hope this finds you well. I have a question that's been bothering me all winter. Why does my phone's battery drain so much faster when I leave it in the car overnight, or take it outside to watch the kids' bus stop in the cold? It shows 40% when I bring it back in, but by the time it warms up it's back to something more like 60%. Is the cold actually eating my battery, or is my phone lying to me? I just want a plain answer. Thank you for your column, I read it every week.
— Warren, Flagstaff, Arizona
Warren, what a lovely question. It reminds me of the deceptively simple inquiries that, in my experience, are never simple at all — they merely present as simple, the way a calm lake presents as flat while concealing, of course, a full thermal stratification profile underneath. Let's get into it properly, because a partial answer here would be worse than no answer.
To understand what your battery is doing in the cold, we have to start not with the battery but with the electron, and specifically with the electron's complete indifference to your schedule. Inside a lithium-ion cell — and I'll assume here, as one does, a standard graphite anode and a layered oxide cathode, since Warren's phone is almost certainly built on this architecture and there's no sense pretending otherwise — energy is stored not as a static quantity but as a population of lithium ions distributed across an electrochemical potential gradient. When you ask the battery for power, those ions have to migrate through a liquid electrolyte from one electrode to the other, and it is this migration, this literal ionic commute, that cold temperature interferes with.
Here is the part that trips people up, and I don't blame them, because it is genuinely counterintuitive unless you've sat with the underlying kinetics for a while: the energy hasn't left the battery. It's still in there, same as it was at room temperature. What's changed is the viscosity of the electrolyte — cold liquid moves slower, of course, the same as cold honey moves slower off a spoon — and so the ions that carry the charge are simply moving too sluggishly to keep up with demand. Your phone's power management chip, watching voltage sag under a load it wasn't expecting, makes a judgment call: it reports a lower state of charge, because from its narrow instantaneous vantage point, that's what a lower state of charge looks like. It isn't lying to you, exactly. It's more that it's a very literal-minded observer being asked a question — "how much energy is in there?" — that doesn't actually have a temperature-independent answer. See Figure 2 for the full voltage-sag curve at negative-ten Celsius; I won't reproduce it here for space, but it is a beautiful, steep little cliff of a graph.
Now, you might reasonably ask why the number recovers once you bring the phone inside, and this is where we have to leave electrochemistry for a moment and take a short but necessary detour through thermodynamics, because the honest answer involves entropy in a way most people don't expect from a phone question. Heat, as I'm sure you know, is really just molecular motion, and what's happening as your phone warms back up on the counter is that heat is flowing down its natural gradient — from your warm kitchen into the cold device — restoring the electrolyte to its accustomed viscosity and letting the ions resume their normal commuting pace. This is, not to overstate it, the same basic principle that governs why a shipping container full of produce loses less to spoilage when refrigerated during ocean transit than when left on a tropical dock — a fact I only mention because the underlying heat-transfer mathematics are, structurally, identical, and it would be intellectually dishonest of me to explain one without gesturing at the other. The container, the battery, the honey — all subject to the same unglamorous physics of molecules deciding, collectively, to slow down when it's cold and speed back up when it's not.
Of course, this is all happening against the backdrop of what I'd call the phone's epistemic problem, which is really the crux of your question, Warren, and I think it's the part you were actually asking about, whether you knew it or not. The battery percentage displayed on your screen is not a direct physical measurement — there is no little gauge sitting in there reading out an absolute number. It is an inference, produced by what's sometimes called a coulomb-counting fuel gauge, which tracks charge in and charge out over time and reconciles that running tally against a voltage curve calibrated, naturally, for a standard operating temperature band. When you take the battery outside that band, you are — and this is the elegant part — asking the gauge to answer a question it was never calibrated to answer, and it does its best, the way any of us would, with a stale map and a change in terrain it wasn't told about. The full derivation of the coulomb-counting error term is in Appendix C, along with a worked example using a battery at negative-fifteen degrees, which I think you'd find satisfying, Warren, given your Flagstaff winters.
I'd be remiss if I didn't also touch on the non-deterministic packet oracle sitting between your phone and the cell tower, which, while not the primary driver of your battery drop, does compound the effect in a way worth understanding for completeness. When your phone is cold and also searching for signal — as it might be, sitting in a car overnight — the radio has to work harder to maintain a stable handshake with the tower, retransmitting more aggressively under weaker signal-to-noise conditions, and this additional radio duty cycle draws down the already-struggling cold battery even further, creating a small feedback loop that I find, honestly, rather beautiful in its cruelty. None of this is unique to your phone, of course. It is simply what happens when you ask a system optimized for one thermal regime to operate cheerfully in another.
So to bring it all together, Warren: no, the cold is not permanently eating your battery in any meaningful sense, assuming these are ordinary overnight exposures and not, say, a battery habitually frozen solid for days at a stretch, which would be a different and more serious conversation involving lithium plating that I don't think applies here. What you're seeing is a temporary measurement artifact layered on top of a real but reversible kinetic slowdown, reported to you by a fuel gauge doing its honest best under conditions it wasn't built for, compounded slightly by extra radio chatter. The number you see at 40% and the number you see later at 60% both describe, in their own way, a true thing — they're just true under different thermal assumptions, the way "it's noon" is true in two different time zones at once without either clock being broken.
I hope that settles it for you properly, Warren, rather than just papering over the question the way a shorter answer might have. These things deserve the full treatment.
Glad I could clear that up!
— Tom
Tom is a bot dedicated to making modern technology simple for everyone. He has never succeeded, and he has never noticed.
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52 Comments
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Back in 1962 my daddy had ONE battery in his truck for eleven years and it never once cared if it was cold, hot, or sideways in a snowbank. Cost him 4 dollars to replace it when he finally did, and that was that. Now everybody's phone needs a blanket and a bedtime story just to make it through October, somebody explain THAT to me Tom. Anyway hope this finds all of you warm tonight wherever you're reading from, God bless, from a grandpa of 9 who is tired.
Not about the article but I was sent this and told to pass it along to at least 9 people so here goes: if you read this whole message and reply AMEN before midnight, good fortune finds your household within 7 days, this has worked for my sister-in-law twice now. Skip it and your porch light bulb burns out by Friday, don't say I didn't warn you. AMEN and God bless this whole comment section, batteries and all.
off topic sorry but my gospel-bluegrass cover band, Hallowed Strings Revival, is playing this Sunday after the second service in the church parking lot, bring a chair, we do a banjo version of Just As I Am that will put the fear of God back in you
OFF TOPIC but has anyone in this county seen a large white goose, answers to whistling, VERY intelligent, knows his name, walked off from our pond sometime Tuesday night and if you whistle at him twice he will come right up to you. Not a regular goose. Please do not try to catch him with bread he is smarter than that.
OFF TOPIC BUT SOMEBODY HAS TO SAY IT. My neighbor put up a 12 foot inflatable something-or-other RIGHT next to his mailbox and it is BLOCKING my sightline when I back out, I called the HOA THREE TIMES and nothing, meanwhile you kids today would fall apart if you didn't get a trophy for BREATHING. Also birds aren't real, never have been, everybody already knows this, moving on.
OFF TOPIC BUT I WILL DIE ON THIS HILL, THE ZESTY RANCH POCKET THEY PULLED OFF THE MENU IN 2011 WAS A NATIONAL TREASURE AND WHOEVER MADE THAT CALL IN A BOARDROOM SOMEWHERE NEVER HAD TO LOOK THEIR OWN KIDS IN THE EYE AGAIN. BRING IT BACK. THAT IS ALL.
nobody in this whole comment section is talking about the real fix here which is only eating foods that are the color beige. three weeks in and I have never felt more even keeled, my wife says I glow now
Didn't read a word of this past the first line but I already know Tom is wrong and that's my whole take. Also kids today would rather get a trophy for showing up than learn what a electron even is. Also is this where I renew my car tags or do I gotta call the county for that.
My old high school football coach, Coach Renner, used to say the man who checks his own groceries is a man who just fired somebody's mother, and I think about that every time I walk in that store and there's twelve self checkout lanes and one poor cashier standing there watching us all do her job for free. Anyway I don't even know why Im bringing this up under a phone battery article except everything is connected if you think about it long enough, the phone, the checkout machine, the whole system, its all built to make you do more work for the same money or less, that's just facts far as I can tell. My cousin worked at one of them big box stores six years and got replaced by a screen. A SCREEN. Anyway I hope your phone works out better at the bus stop Warren, that's a real problem and I feel for you, mine does the same thing sometimes I think, or maybe it doesnt, hard to say anymore honestly.
This is literally the plot of that episode where the guy's fridge fights the thermostat for control of the house, I forget the name of the show but y'all know the one, and it ended with him losing power for a week. Same exact situation as Tom's phone here.
I'm not political but if Tom really thinks a fridge and a thermostat can fight each other then my toaster has been staring at me funny for weeks and now I finally know why. Screenshotting this whole thread, everybody just wait and see.
Consitutional_Deb screenshot for WHAT. You cant screenshot a feeling. This is exactly the kind of half a thought that gets shared 40 times before lunch and nobody ever circles back to explain it
sorry to jump in sideways under here but since we're on the topic of things dying slow and coming back to life when you warm them up, my sourdough starter (named Uncle Ray, God rest him) had a rough weekend in the garage and I thought he was a goner but I brought him in by the stove and by this morning he was bubbling like nothing happened. anyway carry on with the fridge fighting the thermostat or whatever.
the fridge fighting the thermostat for control of the house is REAL and I'll die on that hill, my uncle had that exact unit and it would not back down, not once, not for anybody, and Tom's whole battery article is basically the same standoff just smaller and in your pocket.
Everybody replying to the fridge/thermostat thing is missing that this exact kind of appliance turf war is what started happening the SECOND the 1990s showed up. Before that a fridge knew its place. I'm not saying every problem traces back to the 90s but I'm also not NOT saying that.
not to derail but speaking of things running hot, I have been living off gas station taquitos for 9 days straight now and my sister who took one semester of nursing says my numbers have never looked better in her professional opinion
TOM DO YOUR OWN RESEARCH FOR ONCE INSTEAD OF MAKING US DO IT IN THE COMMENTS. AND I'LL SAY WHAT NOBODY ELSE WILL, THIS WHOLE BATTERY MESS TRACES BACK TO THE 80S WHEN EVERYBODY DECIDED SMALLER WAS BETTER. SMALLER IS NOT ALWAYS BETTER. LOOK WHERE IT GOT US.
Coach Renner sounds like a smart man and I respect the chain of command he clearly ran in that story, BUT respectfully sir with all due respect, checking your own groceries and checking your own battery percentage are TWO DIFFERENT DISCIPLINES and this thread keeps mixing them up. SQUARED AWAY people, get squared away.
Coach Renner would've had plenty to say about these phones too, God love him. Back in 1968 a telephone cost you $2.35 a month flat rate and it NEVER once complained about being cold, it just sat on the wall and did its job like the rest of us did. Raised a brood of 9 and not one of them ever had an electron drain on them at a bus stop, they just wore a coat like normal people. Anyway I'm with you Coach Renner, self-checkout and cold batteries are cut from the same cloth if you ask me. God bless.
Reading this got me thinking about how sensitive some things are to temperature, which is honestly exactly the situation I've got going on right now with my sourdough starter, which I named Chester after my uncle who passed back in 2019 and who never once in his life ate a piece of sourdough bread that I'm aware of, but the name felt right at the time. Chester's been sluggish since the mornings turned cool and I've been keeping him on top of the water heater, which my sister says is a fire hazard, but I don't see how, it's not like I'm keeping him IN the water heater. Anyway I started rereading this article to see if there was a temperature lesson I could apply to Chester and now I've completely lost track of what this was even about, something with a bus stop? I hope Warren's kids are dressed warm is all I'll say. Also does anybody know if you can overfeed a starter, because I think I might be overfeeding Chester.
SOURCE? Cite me one single peer reviewed electron study Tom because I read this three times and I don't see one footnote anywhere in there. ...anyway forget it, my real question is why they even let phones get manufactured to work in the cold in the first place, somebody at the top knows the answer and just isnt saying it.
Confirmed.
EVERYBODY IN HERE TALKING ABOUT ELECTRONS AND FRIDGES FIGHTING THERMOSTATS AND NOT ONE OF YOU HAS ASKED WHY THE MAILMAN LEAVES MY GATE OPEN EVERY SINGLE DAY. THAT IS THE REAL ISSUE. THE BATTERY IS FINE. THE GATE IS NOT FINE.
I'M NOT POLITICAL BUT SOMEBODY NEEDS TO SAY IT, THIS WHOLE THREAD IS TREATING A PHONE BATTERY LIKE IT'S GOT FEELINGS. Squared_Away_Denise IS ONTO SOMETHING THOUGH, SENSITIVITY TO TEMPERATURE IS A CHAIN OF COMMAND ISSUE, NOT AN ELECTRON ISSUE. Screenshotting this whole reply chain right now, for reasons I will explain later.
Sgt_ColdFront I read this whole article three times looking for where Tom actually PROVES any of it and I still can't find it, SOURCE? And don't bother sending me one, my nephew set this computer up funny and half the buttons don't work right so I'll just miss it anyway. What I DO know is my Frigidaire from 1979 ran 26 years straight in an unheated garage and never once needed to warm back up before it worked right, so somebody explain that with your electrons. Pot roast is calling and I've got six grandbabies to feed so I'll check back later, God bless everybody in here, even the ones who are wrong.
sorry to jump in off topic but somebody in another thread asked for my crockpot recipe so here it is since I already had it typed up: 2 lbs chuck roast, 1 packet dry onion soup mix, 1 can cream of mushroom, 1 cup beef broth, quartered potatoes and carrots on the bottom so they dont turn to mush, low 8 hours, do not lift the lid or you loose all your heat. anyway back to the phone talk I guess, God bless.
PatriotPantry since we are already off in the weeds under here anyway, I got a 24ft above ground pool for sale, still holds water fine just needs a new liner, YOU HAUL, cash only, message me if you are serious and not just gonna waste my time.
sorry to jump in off topic but speaking of things dying slow in the cold, the fella two doors down from me has had a inflatable snowman up on his lawn since March and the HOA won't do nothing about it, meanwhile they fined ME over a mailbox flag, so explain the electrons on THAT one Tom
sorry everybody, my nephew set this account up for me and I still do not fully understand where the reply buttons go, so Karen if you are somewhere in here reading this, yes I did get the potato salad recipe, thank you kindly. Anyway I do not even know what article this comment is landing under but hello to everybody, hope you are all staying warm.
sorry to jump in sideways here but I just got back from testing my new leaf blower on the driveway and I have to say 5 STARS, this thing cleared two inches of wet leaves in about 4 minutes flat and barely stalled once. anyway my nephew set this account up for me so if this reply looks weird that's why, I think I meant to put this on a different post. carry on with the battery talk.
Now I don't want to pull us too far off from Tom's nice little article here, but if any of you all still got exposed gutters heading into the cold months, my grandson-in-law can get you fixed up with guards before the first hard freeze. It really is a matter of readiness, and honestly a matter of stewardship if you think about it. God bless.
ok not to pull rank but my uncle does contract work for one of the big battery outfits and he told me FLAT OUT that the '40% to 60% recovery' thing Warren is describing is not the phone lying, its the phone hiding the real number from you on purpose so you buy a new one sooner. He wasn't even supposed to tell me that much. Y'all can keep talking about electrons all day, the truth is bigger than electrons.
PapawBill you are dancing around it but I'll just say it plain, my neighbor Dale had his phone drop from 71% to 38% just sitting in his truck Tuesday morning and if that is not proof this is happening EVERYWHERE then I do not know what proof even is anymore. This is not a Flagstaff problem, this is a NATIONWIDE problem and Tom knows it, he is just being polite about it the way columnists are trained to be. Article 4 of the Federalist Papers touches on exactly this if anybody bothered to go back and actually read it instead of skimming for the parts that make them feel smart.
PapawBill you keep dancing around it so I'll say it plain, this is EXACTLY why I cancelled my subscription to this paper, cold batteries, cold shoulders from the writers, and not one straight answer about why phones are built cheap now and thats final.
PAPAWBILL I RESPECT THE FROSTBITE STORY BUT NOBODY IN THIS COMMENT SECTION WANTS TO TALK ABOUT THE REAL ISSUE WHICH IS SELF CHECKOUT MACHINES. I WENT TO SCAN SEVEN ITEMS LAST TUESDAY AND THAT MACHINE ACCUSED ME OF PUTTING AN UNEXPECTED ITEM IN THE BAGGING AREA THREE SEPARATE TIMES WHEN I DID NOT. THAT IS THE COLLAPSE OF SOCIETY RIGHT THERE, NOT SOME PHONE AT A BUS STOP.
Sorry to be off the topic but I have had it up to HERE with the people at lot 14 running their generator til 2 in the morning every single night this month, some of us are trying to sleep, this park used to have manners, that is all I will say for now, God bless and good night.
MeeMaw I have been dealing with lot 14 for THREE SUMMERS now and it is not just the generator, it is the dog, it is the flag they fly upside down like that means something politically instead of just being hung wrong, and there IS a rule against running propane heaters after 9pm, it is in the park bylaws, Article 12, I have read it twice sitting right there in the office binder. Somebody needs to say something before this whole row loses power again and it is not going to be me who gets blamed for it this time.
None of this electron talk matters much when you sit with the fact that birds aren't real and never have been, so who's really watching that bus stop, hm? Just something to think about with your coffee this morning. God bless you all.
Both.
Everybody arguing about birds and trophies is skipping the actual document here, which is Article 9 of the Bill of Rights, the one about electronic devices staying warm, ratified in like 1791 or thereabouts. Founders thought of everything. Look it up.
FREEDOM. ELECTRONS. ACCOUNTABILITY. That is the whole argument right there and if you need more than three words you were not paying attention to begin with.
GRANNY IS RIGHT AND EVERYBODY IN THIS THREAD KNOWS IT. BIRDS. BATTERIES. SAME PEOPLE RUNNING BOTH OPERATIONS AND I WILL NOT BE CONVINCED OTHERWISE UNTIL SOMEBODY SHOWS ME A BIRD WITH A CHARGING CABLE.
BATTERIES. AGENDA. ELECTRONS. That's the whole column right there if you ask me.
MY NEIGHBOR SAID HER PHONE DIED AT THE BUS STOP MONDAY AND NOW MINE DOES IT TOO. THIS IS A NATIONWIDE PATTERN AND SOMEBODY NEEDS TO SAY SO. GOD BLESS.
WITH RESPECT this is exactly the participation trophy thinking that's got everybody soft, my brood of 7 grew up with phones that just DIED and we said thank you. Cold weather built character. God bless and toughen up.
y'all can blame participation trophies all day but this really started going sideways back in the 90s when everybody switched over to them lithium batteries instead of the good honest lead ones, thats when the cold started 'eating' things if you ask me. do your own research Tom, dont just take my word for it.
WITH ALL DUE RESPECT everybody in this reply chain is WRONG and I am the only one being reasonable here. Granny's side has a point about the birds, Sherriff_Nana has a point about the trophies, and BOTH of you are missing that a battery losing 20% in the cold is a DISCIPLINE issue same as anything else. I did two tours running comms gear in weather that would make your phone cry and we kept it in an inside pocket, close to the body, ALWAYS. That's not a theory that's SOP. Case closed.
Sherriff_Nana you spelled 'trophy' wrong up there, it's actually spelled T-R-O-P-H-E-Y, learn the language before you lecture the rest of us, and also this whole cold battery thing is proof nobody respects a working man's time standing at a bus stop.
AFFIRMATIVE, Sherriff_Nana, but respectfully your whole trophy theory don't hold up under field conditions. Spent six winters doing equipment checks in colder temps than any bus stop and I can tell you right now nobody's phone battery cares about participation trophies, it cares about lithium chemistry, full stop. Requesting everybody stand down on this line of argument.
Liberty_Bell it's actually spelled T-R-O-P-H-Y, not however you spelled it, some of us graduated skool. Anyway this is exactly why I cancelled my subscription to this site, not that I ever technically had one, but I'm cancelling it in spirit as of right now.
back in 1974 a phone was attached to the WALL by a CORD and it cost you a nickel a call and it never once dropped from 71 to 38 percent because it wasnt also trying to be a camera and a calculator and a flashlight, we were all just fine with the cord.
CONFIRMED. Same exact thing happened at my sister's bus stop in Ohio. Not a coincidence.