How Long will the Battery Last

Submitted: Friday, Jan 28, 2005 at 22:37
ThreadID: 19873 Views:1650 Replies:4 FollowUps:6
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Hi,
Just a nice simple question.
How long would a car battery last running a laptop say playing DVDs or watching TV. The Laptop has these specs; 20v @ 4.5 amps = 90watts (right or wrong)
What sort of life out of a battery would you expect.

Cheers
Only 11 days to go................................
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Reply By: John - Friday, Jan 28, 2005 at 23:12

Friday, Jan 28, 2005 at 23:12
Dear Craig
Its not such a simple question. The 90W quoted is propably the 240V adaptor maximum consumption.
Depending on how you power it (invertor or a direct voltage convertor) .my guess is you will use about 30W on average. This is only a guess and I dont have any direct experience. Can you use a multimeter to measure the consumption ?
Assuming 30W is correct a 75 AHr battery has about 75 X 13= 975 What hours of power, but rember if its a normal car battery it wont have a long life in a deep cycle application even if you limit it to 50 % discharge. A car alternator will also only charge to about 80%.
Short answer (with lots of variables) about 24 hours to completly flat. But with a very short bat life.
If you limit to about 10 hours you would get a couple of years out of a starting battery.
Sorry to be vague, but there are lots of variables. Hope this helps
Cheers John
AnswerID: 95464

Follow Up By: Member - Craig M (NSW) - Friday, Jan 28, 2005 at 23:27

Friday, Jan 28, 2005 at 23:27
Thanks for the info.
So even at a rough estimate it wont hurt or flatten the battery if it is used say for 2 to 3 hours at a time.
It is getting run off a adptor, plugged into the cig lighter.

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FollowupID: 354219

Follow Up By: John - Saturday, Jan 29, 2005 at 00:17

Saturday, Jan 29, 2005 at 00:17
Dear Craig
2 or 3 hours should be fine. Try and run with the ignition off or on acc. Turn off the ignition completly when finished.
If you are in a remote location running accessories off any battery that is used to start the car is always a little risky and I would be thinking of a second battery or portable pack as insurance.
Cheers John
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Reply By: Member - Brian H (WA) - Saturday, Jan 29, 2005 at 00:32

Saturday, Jan 29, 2005 at 00:32
I have to agree with John. It also depends on the capacity of the battery. Bigger batts will last longer. I have an aux batt in the cruiser and it runs my fridge for about 18 hours before it trips off. There's also a seperate batt in the camper. Expensive to set up but you have to keep the important stuff cold and the kids out of your hair.
If in doubt, talk to an auto sparky.
Cheers, enjoy the hols. Keep us posted.
AnswerID: 95473

Reply By: ptcrowe - Saturday, Jan 29, 2005 at 19:46

Saturday, Jan 29, 2005 at 19:46
How long is a piece of string?
AnswerID: 95555

Follow Up By: Member - Blue (VIC) - Saturday, Jan 29, 2005 at 21:43

Saturday, Jan 29, 2005 at 21:43
Twice as long as it is from one end to the middle...
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Follow Up By: Member - Craig M (NSW) - Sunday, Jan 30, 2005 at 00:41

Sunday, Jan 30, 2005 at 00:41
Use a Tape Measure :-)
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Follow Up By: TheUndertaker - Sunday, Jan 30, 2005 at 18:18

Sunday, Jan 30, 2005 at 18:18
As long as it needs to be.
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FollowupID: 354462

Reply By: Baz (NSW) - Saturday, Jan 29, 2005 at 20:04

Saturday, Jan 29, 2005 at 20:04
I don't know how long it would last but i can tell you that you will be able to watch 3 DVDs no problem from it, how do i know i hear you ask well we have done it.

The battery in question is a 75 A/H Deepcycle and the laptop we use is 240V only so we use a 300Watt pure sinewave inverter to power it, we get 2 hrs out of the laptop battery trouble is most DVDs are longer than 2 hrs.

Hope this helps,

Baz.
AnswerID: 95557

Follow Up By: Member - Craig M (NSW) - Sunday, Jan 30, 2005 at 00:43

Sunday, Jan 30, 2005 at 00:43
Thanks for the info,
I think also using a inverter would drain more as well, as I read the other day they draw a certain amount when switched on.
Not sure if I would get the length of a DVD out of my battery either, will have to try it out.

Cheers
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FollowupID: 354371

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