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Jumping a big car with a small one

Mike Gayner

Mike Gayner

Diamond Member
Last night I accidentally left my keys in the ignition and now my BMW 540i is stuck in the garage with a flat battery. My fiancée's car is a little 1.6l Suzuki with a tiny battery. My BMW's battery weighs as much as her entire car. Am I going to be able to jump start my car with hers, or is that gonna lead to trouble?
 
Both use the same voltage (12V)? Then yes you can jump it, it just takes longer. Hook it up, start the Suzuki, and wait a few minutes. Rev the engine a bit if it makes you feel better.

Remember: positive to positive; negative to negative
 
IronWing said:
Both use the same voltage (12V)? Then yes you can jump it, it just takes longer. Hook it up, start the Suzuki, and wait a few minutes. Rev the engine a bit if it makes you feel better.

Remember: positive to positive; negative to negative
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Oh voltage is the only thing that matters? Sweet, I'll just start it with this then:

FNOTWKCF5HVPBSH.MEDIUM.jpg


🙄
 
It will start it, just let the little suzuki run for a while with the cables connected to give the BMW's battery some time to build up a charge. The Suzuki's battery and it's charging system may not be up to the task of starting the BMW directly but it will be plenty to build up a charge in the BMW's battery if you give it some time.
 
Bignate603 said:
It will start it, just let the little suzuki run for a while with the cables connected to give the BMW's battery some time to build up a charge. The Suzuki's battery and it's charging system may not be up to the task of starting the BMW directly but it will be plenty to build up a charge in the BMW's battery if you give it some time.
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Yup, did this and started eventually, after a couple of failed attempts (the Suzuki definitely isn't up to starting the BMW directly). Took around 5-7mins in the end. Thanks.
 
Mike Gayner said:
Yup, did this and started eventually, after a couple of failed attempts (the Suzuki definitely isn't up to starting the BMW directly). Took around 5-7mins in the end. Thanks.
Click to expand...

Sounds like everything worked out well then, I've jumped relatively large trucks with tiny little cars like this before. It takes a while (especially when it's ridiculously cold out) but I've never had one completely refuse to start.

Quick question though, what stays on if your keys are in the ignition? I know BMWs have more electronics than most cars but I'm a bit surprised that it would be enough to kill the battery overnight. It may be worth taking your car to your mechanic or the kiwi equivalent of an Autozone to have them check the battery and charging system.
 
Bignate603 said:
Sounds like everything worked out well then, I've jumped relatively large trucks with tiny little cars like this before. It takes a while (especially when it's ridiculously cold out) but I've never had one completely refuse to start.

Quick question though, what stays on if your keys are in the ignition? I know BMWs have more electronics than most cars but I'm a bit surprised that it would be enough to kill the battery overnight. It may be worth taking your car to your mechanic or the kiwi equivalent of an Autozone to have them check the battery and charging system.
Click to expand...

Yeah I was a little surprised too - though I think the blower fan may have been on. I already know that my battery needs replacing soon - it was around 75% health last time I had it checked about a year ago.
 
Mike Gayner said:
Yeah I was a little surprised too - though I think the blower fan may have been on. I already know that my battery needs replacing soon - it was around 75% health last time I had it checked about a year ago.
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It's probably time then. Fully draining a car battery isn't health for it either. It usually won't flat out kill one but it's just one more nail in the coffin.
 
Mike Gayner said:
Oh voltage is the only thing that matters? Sweet, I'll just start it with this then:

FNOTWKCF5HVPBSH.MEDIUM.jpg


🙄
Click to expand...

actually you could if ya had enough of the them in a series/parallel arrangement so that the voltage and amperage matched that of an auto battery.

it be easier just hooking up the suzuki with the jumper cables like you did.
 
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Mike Gayner said:
Yeah I was a little surprised too - though I think the blower fan may have been on. I already know that my battery needs replacing soon - it was around 75% health last time I had it checked about a year ago.
Click to expand...

Batteries around here (FL) rarely last more than 3 years (heat) and today's cars always have the BCU running and sometimes more. My car (05 Chevy) has a feature called "afterblow", it runs the blower after the car is off to help prevent condensation and mold on the AC evaporator coil. Came out to the car one day and it was doing this, I thought the BCU was broken or something, dealer said nope, it's normal, no wonder battery's never last that long anymore..
 
Bignate603 said:
Except he lives in New Zealand, not Canada.
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Are you aware that every country experiences winter?

In any event, most dead batteries are not caused by "cold" but by things draining the battery. It seems like night time is 23 hours per day in winter, so everyone drives with their headlights on, and this increases the chance of accidentally leaving your lights on.
Last week I tried starting my Corolla after it sat unused for 2 weeks and it wouldn't start. It had enough power to turn over, but for some reason it just wasn't starting. I connected my little battery pack to it and it started easily. If I were in the desert wasteland known as New Zealand, I would be trapped! The car was parked in an area wide enough for 1 car, so jumping from another car wouldn't work. I would actually need to take the battery out of the car, carry it to my other car, charge it, carry it back to the Corolla, then try it. If it doesn't work, repeat that whole process a second time.

Nissans in particular seem to have issues with batteries dying overnight. Something drains the hell out of the batteries and the car needs to be jumped in the morning.
 
ShawnD1... While it might be the case sometimes you might want to re-think it...?

Explanation

  • Extreme cold weather conditions can affect the average automobile battery's life and performance. Automobile batteries produce electrons through chemical reactions. During cold weather, the battery's chemical reactions take place more slowly, thus producing fewer electrons with which to power the engine. In addition, the engine's oil thickens during cold weather, causing the engine to require up to three times as much power to turn over.

Cranking Amps


  • Automobile battery output is usually rated at 77 degrees Fahrenheit. The battery power drops off below this temperature, and at 5 degrees Fahrenheit, a fully charged battery has only half of its rated capacity. The cranking amp or CA rate helps determine how much power can be delivered to start an automobile in most climates. The CA rate indicates the discharge load that a new, fully charged battery can deliver at 32 degrees Fahrenheit.

Cold-Cranking Amps


  • The cold-cranking amps or CCA rating indicates a battery's ability to start an engine in extremely cold weather. The CCA rate measures the discharge load delivered by a battery at 0 degrees Fahrenheit. In normal weather conditions, a battery with a low CCA will reliably start any automobile, but in cold climates, the amount of energy needed to start an automobile engine can exceed the energy available from the battery. Choosing a battery with a high CCA rating is beneficial if you live in a cold climate.



Read more: The Effect of Cold Weather on AVG Automobile Batteries | eHow.com http://www.ehow.com/about_6326114_effect-weather-avg-automobile-batteries.html#ixzz1epzy8Eq3
Click to expand...
 
ShawnD1 said:
Are you aware that every country experiences winter?
Click to expand...

Are you aware that the severity of winter differs greatly depending on where you are? If you bothered to do a web search you'd find the location that the OP lists has an average temperature during the winter in the low 40's F. Talking about -30 doesn't really mean much for where he lives.

In any event, most dead batteries are not caused by "cold" but by things draining the battery.
Click to expand...

While cold doesn't kill batteries it makes you notice when they're dying. The cold slows down the reaction inside the battery so if the battery is starting to die it will have trouble starting the car when its cold much sooner than if the battery was warm. That's why you see tons of people with cars that won't start when you have a sudden drop in temperature, the batteries were strong enough to start the car when they're warm but when the temp drops the reaction is slowed enough that they can't get the car going.

Last week I tried starting my Corolla after it sat unused for 2 weeks and it wouldn't start. It had enough power to turn over, but for some reason it just wasn't starting. I connected my little battery pack to it and it started easily. If I were in the desert wasteland known as New Zealand, I would be trapped! The car was parked in an area wide enough for 1 car, so jumping from another car wouldn't work. I would actually need to take the battery out of the car, carry it to my other car, charge it, carry it back to the Corolla, then try it. If it doesn't work, repeat that whole process a second time.
Click to expand...

It's called pushing the car. You've never seen someone in a parking lot push a car out of a spot so they could get it close enough to another vehicle to jump it? They do it all the time.
 
While cold doesn't kill batteries it makes you notice when they're dying.
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This is very true. What's nice is that you'll tend to notice this BEFORE leaving your house. The car has been sitting all night, slowly draining away to the security system and stuff. Early in the morning also seems to be the coldest part of the day, so it's least likely to start. Try to start the car. It won't start. Stranded, but stranded at home is better than stranded at Walmart.
Anyway, my point is that a battery able to start in the morning will probably also start after you've driven the car around and the engine is warmed up. If you could start the car and drive it to work, it likely won't die at work unless you left the interior lights on or something else that drains power.



Bartman39 said:
ShawnD1... While it might be the case sometimes you might want to re-think it...?
Click to expand...
Here's a picture I posted last year. It's the outside temperature display in my Corolla
28ca.jpg

It was -28C (-18F) and the car would cold start easily, and it was like that all winter. Whatever temperature it was, that Corolla would start.
Last week, that same car with the same engine and the same viscosity oil and a nice fresh (couple months old) battery would not start at -5C (+23F). Letting the car sit for 2 weeks kills the battery a lot more than the coldest day of winter.

I still like to keep that battery pack with me. I don't want to be stranded because of something silly like leaving the heated seat on when the car is not running.
 
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