How long will the car battery last?

[imported_goku]

OK, I'm currently working on my laptop via a power inverter hooked into the cigarette lighter. I've had the laptop running for about an hour now and I was wondering, how long can the battery last before it becomes too drained to be able to turn on the car? Does the car battery have a lot of power or is an hour usage of power going to pretty much have used it's power capacity? Typical MAH of a car battery? How low can it go before it's too low? The car doesn't have a voltage guage on the dash.

 

[akubi]

why don't you turn the car on and let the alternator do it's job?

 

[imported_goku]

Are you telling me I'm going to have my car idle for 3 hours? You've got to be kidding.

 

[jtvang125]

If the battery is in good condition it should last about an hour or two. Just start the car every 30 minutes or so and leave running for about 10mins.

 

[Pepsi90919]

7 minutes 8 seconds

 

[ValValline]

A car battery's job is to start the car, maintain radio presets, ECU and diagnostic information, time, etc. Nothing more.

Most car makers specify a battery with a large reserve for people who leave lights on or run accessories (like a laptop). But there are too many variables (eg age/condition of the battery, current temp, state of charge prior to shutting the car off, etc) to predict how long it will last before it can no longer start the vehicle.

 

[DrPizza]

Depends on the specific battery your car has as well as how old the battery is. Marine batteries would last much longer than the typical car battery for that type of application. Simple way to figure it out: drain your battery completely using your laptop. Hook the battery up to a battery charger. Multiply the amps on the charger by the time it takes to fully charge the battery... this will give you the number of amp hours you have. Multiply this by 80%, since the charger won't have perfect efficiency. Then, using the number of amps your laptop draws, divide the amp hours by that number and you'll have the amount of time your battery will last. (That's the complicated way) How about this: just use the laptop, then have someone give you a jump-start if the car won't start on its own. You do have jumper cables in the trunk, right?

 

[tfinch2]

Did your parents pay for a dedicated DSL line out to the car too?

 

[clickynext]

I wouldn't count on the car battery to last too long. Why don't you just get a spare laptop battery? Less trouble than if your car battery runs out in a bad place.

 

[Zenmervolt]

Originally posted by: jtvang125
If the battery is in good condition it should last about an hour or two. Just start the car every 30 minutes or so and leave running for about 10mins.

Idling for 10 minutes does not even replenish the energy required to start the car, much less the energy used by the laptop. Your method would wear out the battery faster than not starting the car at all.

A lead-acid car battery is not designed to be drained very far. If you drain it to dead, you've lost probably a year of the battery's normal operational life.

You shouldn't use your car as a power station. Not what the battery and electrical system are designed for.

ZV