What NOT to Leave in Your Car in Winter (and Why)

Cars in winter are refrigerators, not storage units. Once the temperature drops below freezing for any stretch, a parked car becomes cold enough to burst cans, kill phone batteries, and quietly wreck medications. Most of the damage happens overnight, when nobody is watching, and most of it is avoidable if you bring the right things inside before the temperature drops.

This is the list to run on the first cold night of the year. Some of it will cost you real money the first time you skip it.

Phones, tablets, and anything with a lithium battery

Lithium-ion batteries lose capacity fast in the cold. Apple publishes a "below 10°C (50°F)" warning on every iPhone; the battery icon drops a few percentage points just from sitting in a cold car overnight, even if you didn't touch it. Below freezing, a charged phone may refuse to turn on, or shut itself off as soon as you try to use it. The damage is usually not permanent. The battery recovers once it warms up. But if your car dies on a winter night and your phone is dead too, you can't call for help.

Two rules cover most situations:

• Bring the phone inside overnight if the temperature is forecast below 20°F.
• A lithium jump pack left in a trunk at -10°F for a week can drop to a third of its rated capacity.

The fix is boring: take the phone inside.

Canned drinks, aerosols, and anything else pressurized

Soda cans, beer cans, and seltzer bottles are the headline example because they burst and leave evidence. A 12-ounce soda has enough water in it to expand by roughly 9% when it freezes solid, and the can is not built to absorb that. The pop, the sticky mess on your trunk carpet, and the smell that lingers for weeks are all avoidable if you bring the cans inside.

Less obvious offenders:

• Glass bottles of carbonated drink can crack at the seam.
• Aerosol cans (deodorant, hairspray, lubricant, brake cleaner) will leak or burst in a hard freeze.
• Windshield washer fluid with a freezing point above the night's low will crack the reservoir.

If you keep sparkling water in the car for camping, that's fine when lows stay above 0°F. Below that, pull the case inside.

Medications, especially insulin and EpiPens

Most oral medications tolerate a cold car for a few hours. A few do not, and the consequences of a ruined dose are not symmetric with the cost of bringing the bottle inside.

The hard cases:

• Insulin loses potency once it freezes. The CDC says do not let insulin freeze. A glove box on a -10°F night is not safe.
• EpiPens and other injectable emergency meds are sensitive to both heat and cold. The official storage range is 59°F to 86°F. A 0°F car is not in spec.
• Inhalers can crack or lose metered-dose accuracy if frozen.
• Glaucoma drops and many eye medications have similar narrow ranges.

The fix is simple: take the medication inside when you get home.

Water bottles and anything else that expands when it freezes

A reusable plastic water bottle left in a trunk overnight is the textbook example. The bottle deforms, the cap cracks, and you get a wet trunk and a wet backpack the next morning. The same thing happens with anything water-based:

• Glass jars of sauce or salsa can crack at the seam.
• Wine bottles with a cork push the cork out, slowly.
• Antifreeze is the one liquid that's fine. It's already formulated for the cold.

A reusable bottle in the cabin is mostly fine. In the trunk, take it inside.

Lithium power banks, jump packs, and USB tool batteries

The chemistry is the same as a phone battery. A 10,000 mAh power bank left in a car at -10°F for a week may drop to half its capacity. A jump pack you needed at 6 AM on a dead-battery morning is exactly the one that didn't survive the trunk.

The worst case is a battery that's both dead and cold. A lithium cell discharged below its safe threshold and then frozen can develop internal plating that kills the cell permanently. A power bank you forgot to top off in October and forgot in the trunk all winter may be a brick by spring.

If you carry any lithium tool in the car (drill, work light, USB fan), bring it inside for the cold stretches.

What stays in the car without worry

A short list of things that don't care about the cold:

• A roll of paper towels.
• A shovel, kitty litter, or traction mats (sand gets hard, but it doesn't break).
• Jumper cables (copper doesn't care).
• A spare tire (designed for under-car temperatures).
• Wool blankets and most synthetic layers. Cotton is the one to avoid. It loses insulation when wet.
• A spare phone charger cable. The cable is fine. The brick may be sluggish in extreme cold.

Theft is a separate question. Don't leave valuables in the car for visibility reasons. This article is only about the cold.

A 30-second routine that prevents all of it

On the first night the forecast calls for a low below 20°F, walk to the car and grab:

• Phones and tablets.
• Cans, bottles, and aerosols.
• Power banks and the jump pack if you have a habit of leaving them in the car.

That routine takes 30 seconds and avoids every failure mode on this list.

For the full kit you should keep in the car to handle a breakdown, see our winter car emergency kit guide. If you're driving in snow and ice, the winter driving guide covers speed, skids, and what to do if you get stuck.

Frequently asked questions

Does cold permanently damage lithium batteries? Not from one cold night. The temporary capacity loss recovers when the battery warms up. Permanent damage comes from a battery that's both discharged and frozen for an extended period.

Can I keep a case of water in my car in winter? Only if the case is rated for the forecast low. Standard bottled water freezes around 0°F and the bottles crack.

Is it safe to leave canned drinks in the car overnight? A can of soda can survive a 30°F night. It cannot survive a hard freeze. The can will split, the trunk will be sticky, and the smell will outlast the soda.