How long can you leave a car door open before the battery dies

2005 Mazda3

I carpooled to work today. I first grabbed something from the trunk of my car, then exited my garage. I was in a rush, and didnt realize i didnt close the trunk till i got to work.

Will leaving the trunk light on for 12hrs kill the battery?

If when you open the trunk lights turn on and stay on, possibly.

It will probably turn them off by itself after an amount of time. I left my Jettas interior lights on last night and they were off this morning and it started up fine.

It will probably turn them off by itself after an amount of time. I left my Jettas interior lights on last night and they were off this morning and it started up fine.

but is the trunk lite on that same circuit?

yeah, thats the interior lites. mine does the same thing.

but is the trunk lite on that same circuit?

I've found modern cars will shutdown the circuit if the battery drops below a certain voltage, enough for it to give it one rescue start.

I've never completely depleted the battery in my car(s).

This happened to my wife's Mazda 3, but the trunk was left open over a weekend in our garage. Come Monday morning it needed a jump start.

It won't "kill" the battery per-se but you definitely should get a battery re-charger and charge that sucker because your car's alternator won't be able to do it. The car's alternator is a battery maintainer, not a charger.

If you have a Battery Saver circuit, then most likely the trunk light will be turned off after 30-45 minutes. If you don't, it will most likely discharge your battery to where the car will not start.

The car's alternator is a battery maintainer, not a charger.

Especially not repeatedly.

it should die, my friends new 09 mazda 3, he left for vegas for 4 days came back no start. same idea if you leave the light on since you have something drawing the battery, and my friend had nothing.

if it did just jump it and leave it on for about an hour to charge up the battery and you should be good to go. Dont worry too much about it.

Many modern cars have what is called an IOD fuse that is to be pulled for storage. Ignition Off Draw. This gets rid of most of the parasitic draw from the battery.

Just remember to install it again.

it should die, my friends new 09 mazda 3, he left for vegas for 4 days came back no start. same idea if you leave the light on since you have something drawing the battery, and my friend had nothing.

if it did just jump it and leave it on for about an hour to charge up the battery and you should be good to go. Dont worry too much about it.

I would be certain something was wrong with my car if it would not start after sitting for just 4 days.

time to get some LED lighting!

The alternator is not designed to charge a dead battery. It is designed to maintain a good charge on the battery. It can recharge a dead battery, but it is not meant to do this.

Especially not repeatedly.

I've charged a few cars with a battery charger that were driven regularly yet had only a 25% SOC. Anyway, it's really hard on the alternator to charge a dead battery and it's just better and more reliable to just use a dedicated battery charger ever so often to ensure that the batteries are fully charged. Car batteries like to be constantly charged, otherwise you get sulfation on the lead plates which means reduced capacity. A decent battery charger can be had for around $50.

I have a mazda 3, I have done this. Answer is....

Yes, it will.

That sucks the other MZ3 owners say it will be dead.

My Nissan turns off the interior lights after like 30 mins or something, if a door is open a crack. I don't know about the trunk though.

Even worse, I think people seriously underestimate how quickly those car alternators can charge a depleted car battery. If the battery is at a state of 0% charge (11.8V when there is no load), when using a wall battery charger, if you charge at 2AH, it will take well over 28 hours to charge that car battery. Cranking the engine takes a significant drain on the battery so the only plausible scenario to ever even consider charging that battery to full would be to have several, long highway commutes. Most alternator's peak output is at 2500rpm, a lot of 4 bangers rev at this speed when cruising on the highway but the cars with bigger engines do not, some cruise at as low as 1500rpm which means alternator output is significantly diminished.

I've charged a few cars with a battery charger that were driven regularly yet had only a 25% SOC. Anyway, it's really hard on the alternator to charge a dead battery and it's just better and more reliable to just use a dedicated battery charger ever so often to ensure that the batteries are fully charged. Car batteries like to be constantly charged, otherwise you get sulfation on the lead plates which means reduced capacity. A decent battery charger can be had for around $50.

I guess if you know your battery is low, you could drop a gear or not use overdrive to get the revs up on the highway, if you have one of those engines that are just loafing along when cruising.

Even worse, I think people seriously underestimate how quickly those car alternators can charge a depleted car battery. If the battery is at a state of 0% charge (11.8V when there is no load), when using a wall battery charger, if you charge at 2AH, it will take well over 28 hours to charge that car battery. Cranking the engine takes a significant drain on the battery so the only plausible scenario to ever even consider charging that battery to full would be to have several, long highway commutes. Most alternator's peak output is at 2500rpm, a lot of 4 bangers rev at this speed when cruising on the highway but the cars with bigger engines do not, some cruise at as low as 1500rpm which means alternator output is significantly diminished.

I've charged a few cars with a battery charger that were driven regularly yet had only a 25% SOC. Anyway, it's really hard on the alternator to charge a dead battery and it's just better and more reliable to just use a dedicated battery charger ever so often to ensure that the batteries are fully charged. Car batteries like to be constantly charged, otherwise you get sulfation on the lead plates which means reduced capacity. A decent battery charger can be had for around $50.

thx for the replies.

got home. trunk lite was still on.

but car started!