How long can a car sit before the battery dies?
A typical car lasts about 2 to 4 weeks parked before the 12V battery is too flat to start. Enter your battery's amp-hours and parasitic draw for a closer estimate.
Estimated time before it may not start
~35 days
In cold weather, expect closer to ~23 days - a battery delivers less when it is freezing, and an older battery even less.
How this is estimated
A starter needs a fairly full battery, so we assume the car may fail to crank once about half the battery's capacity is gone. Days = (Ah × 0.5) ÷ draw in amps ÷ 24. It is a guide only - cold weather, an aging battery, and a higher-than-normal parasitic draw all shorten it, sometimes a lot.
Not sure of your battery's Ah? Convert CCA to Ah → or look up your car's battery →
Frequently asked
How long can a car sit before the battery dies?
For a typical car - a healthy 50 Ah battery with a 30 mA parasitic draw - roughly 30 days before it may be too flat to start, and less in cold weather or with an older battery. Cars with more electronics draw more and last less.
What is parasitic draw?
It is the small current your car uses while parked and off - the alarm, keyless entry, clock, and control modules. Most cars draw about 20-50 milliamps. A stuck relay or aftermarket accessory can push it much higher and kill a battery in days.
How do I stop my battery dying while parked?
Plug in a battery maintainer (trickle charger) if the car sits more than a couple of weeks, disconnect the negative terminal for long storage, or start and drive it for 20+ minutes every week or two.