How Long Can a Car Sit Before the Battery Dies?

Short answer: a healthy battery in a modern car will usually start the engine after two weeks of sitting, and often after a month or more. An older battery, cold weather, or an electrical fault can cut that to days. If the car will sit longer than a couple of weeks, either drive it for 30 minutes at speed once a week, connect a battery maintainer, or leave a charged jump starter where you can reach it when you get back.

This time of year a lot of cars sit: at the airport over Thanksgiving, in the driveway while snowbirds head south, or in the garage until spring. Here's why the battery dies and how to avoid it.

How long a parked car's battery actually lasts

There isn't one number, because it depends on the battery's age and health, the temperature, and how much the car draws while it's off. The sources roughly agree on the range:

• About two weeks, at minimum. The UK's AA says most modern cars with a fairly healthy battery should last at least two weeks without being started, and to start it weekly if you're unsure of the battery's condition (The AA).
• Four weeks to two months. Interstate Batteries puts a sitting battery's life at about four weeks to two months before it dies (Interstate Batteries).
• Recharge every six weeks. AAA Club Alliance says an idle battery slowly loses its charge and should be charged every six weeks to stay at full capacity (AAA Club Alliance).

Treat two weeks as the safe planning number. If you'll be gone longer than that, plan for the battery.

Why a parked car drains its battery

A car that's switched off isn't fully off. The engine computer keeps its memory, the clock runs, the alarm watches the doors, and the keyless entry receiver listens for your fob. This is called parasitic drain, or key-off drain.

Battery Tender, which makes battery maintainers, puts normal parasitic draw at about 20 to 50 milliamps. By its math, a 60 amp-hour battery could in theory sustain a 50 mA draw for about 50 days, but in practice a healthy battery handles several weeks without trouble. Above roughly 75 to 100 mA, the draw is abnormal: at 250 mA, often from a faulty module or a short, a 60 Ah battery can go flat in under 10 days, and at 500 mA in about five (Battery Tender). If your car has gone dead after just a few days parked, that's a sign something is drawing more than it should, and a shop can test for it.

What makes it die faster

• Age. AAA (source) says a battery typically lasts three to five years, and about three in hot climates. An old battery starts with less in reserve, so it reaches "won't crank" sooner. Our guide to the signs your car battery is dying covers what to watch for before you leave.
• Cold. A cold battery delivers less power, and a cold engine needs more to turn over. A battery that would have managed after three weeks in September may not manage after three weeks in December. See how to jump-start a car in freezing weather if it happens.
• Short trips beforehand. AAA notes that batteries in cars driven mostly on short trips may not fully recharge.
• Accessories and alarms. Aftermarket alarms, dash cams wired to stay on, and anything plugged into an always-on 12V outlet add to the drain. Interstate suggests leaving the alarm off if the car is in a secure garage.

How to keep the battery alive while the car sits

For a trip of a week or two

Usually nothing special is needed if the battery is healthy. Before you go:

• Take a longer drive in the days before, not just short errands, so the battery starts full.
• Unplug dash cams, chargers, and anything else in the 12V outlets.
• Make sure every interior light is off and the doors and trunk are fully closed.
• Pack a charged jump starter in the car, or bring one with you (more on that below).

For a month or longer

• Drive it weekly, properly. Interstate recommends driving at least 30 minutes at highway speeds once a week; a quick trip to the store isn't enough. The AA suggests a drive of 15 minutes or more, or running the engine for about 15 minutes once a week. Never run the engine in a closed garage, and never leave it running unattended.
• Use a battery maintainer. For seasonal storage, a plug-in maintainer (sometimes called a tender) keeps the battery topped up without overcharging. Both AAA and Interstate recommend one for cars that sit for extended periods.
• Fill the tank. The AA suggests topping up the fuel before a long layup, since a full tank attracts less condensation.
• Think about the brakes and tires. The AA notes that a parking brake left on for a long time can seize, and advises checking tire pressures before you drive after a long layup.
• Hybrids have a 12-volt battery too. The AA suggests putting them in "ready" mode for about 10 minutes a week. EV owners should check the manual for how the 12-volt battery is kept charged.

Motorcycles, ATVs, and the lawn tractor

Powersport batteries are small and drain fast over a winter. The POD X Motorcycle Battery Tender Cable ($14.95) is a quick-connect 12V lead that installs once on the battery's ring terminals and stays on the bike, ATV, UTV, snowmobile, or lawn tractor. After that you can plug in a standard SAE tender charger, or a POD X XTREME jump starter, without pulling the seat or panels. More in our powersport jump starter guide.

Your backup plan: a jump starter that holds its charge

Even with good habits, the car in the airport long-term lot might not start when you get back. A portable jump starter means you don't need another car or a wait for roadside service.

The POD X XTREME 1000A Jump Starter ($129.99, in stock) jump-starts 12V vehicles without a second vehicle and delivers 20 or more jumps per charge. Its Intelli-Jump smart clamps block sparks, reverse polarity, and short circuits: connect the clamps, wait for the green light, and start the engine. It also works as a USB power bank, and the built-in LED doubles as a flashlight, strobe, or SOS beacon.

Here's what matters for a parked car: the POD X FAQ says it holds a charge for months, and recommends topping it up every three months and after every use (POD X FAQ). The FAQ also recommends keeping it in the cabin rather than the trunk in cold weather and warming it before use, since lithium loses some capacity when frozen. Flying out? The FAQ says POD X jump starters can go in carry-on luggage, never checked; see can you bring a jump starter on a plane for the details.

If you also want a hands-free light for an early-morning start in a dark lot, the POD X Truck Kit bundles the XTREME with the Port-A-Bull Tripod Flashlight for $169.

New to jump-starting? Our step-by-step jump-start guide walks through it for 12V vehicles.

After the car starts

A jump doesn't refill the battery, so drive for a good while before shutting it off. AAA warns that letting a battery go completely dead takes a big chunk out of its life, so if it dies again soon, have the battery and charging system tested.

Quick checklist before you leave the car

• Battery is less than a few years old and shows no warning signs.
• Took a longer drive in the days before parking.
• Dash cams and 12V accessories unplugged, interior lights off.
• Gone longer than two weeks? Arrange a weekly drive or connect a maintainer.
• Charged jump starter in the cabin, or in your carry-on.

Every POD X product carries a 3-year warranty with free registration (POD X FAQ), and US orders of $50 or more ship free.