[Glen e]

As I read the owners manual, it says that if I’m trying to jumpstart the where the BMW is the receiver you use the under hood posts. But how about the converse, where I want to use the BMW as the source to jump a dead car or a bike?

The under hood terminal posts go both ways, right?

Thx!

[T0RM3NT]

Originally Posted by Glen e

As I read the owners manual, it says that if I’m trying to jumpstart the where the BMW is the receiver you use the under hood posts. But how about the converse, where I want to use the BMW as the source to jump a dead car or a bike?

The under hood terminal posts go both ways, right?

Thx!

Uh, what!? Are you serious or am I missing the point of your question?

[Glen e]

What’s so stupid about this question? Do the post go both ways? They’re just a connection to the battery , correct?

[atek]

Originally Posted by T0RM3NT

Uh, what!? Are you serious or am I missing the point of your question?

He's wondering if you can use the underhood supplied posts for positive/negative to jump another car.

Ie:

BMW -- jumping -- >> another car

and since the BMW batteries are in the trunk, you would normally have to use the given posts under the hood in the engine bay.


In short, OP. It may work. The issue is the power draw, or voltage drop seen from the long distance + peripheral posts. Your best bet in that method is to pop the trunk and hook it up directly if applicable. Or better yet just buy a battery jump pack. They are really cheap these days and can save you a lot.

[T0RM3NT]

Originally Posted by Glen e

What’s so stupid about this question? Do the post go both ways? They’re just a connection to the battery , correct?

No one said the question was stupid...I wasn't sure I understood the question. I would think they are just remote battery terminal posts under the hood. However, is there any potential to damage other components when using those remote battery terminal posts? That I'm not sure of. So, a good question that I didn't completely understand.

[Pauldunlop13]

Since there is no battery under the hood, those posts are 100% there to provide easy access to jump your car or someone elses

they were put there for your convenience

[snowbimmer]

Originally Posted by Pauldunlop13

Since there is no battery under the hood, those posts are 100% there to provide easy access to jump your car or someone elses

they were put there for your convenience

My battery died a couple weeks ago. I was talking to my service guy about this very thing. The manual only talks about using another car to jump your BMW. He said it works fine the other direction too.

[ro881e]

This is literally what they are for. I recall reading that you should never attach anything directly to the battery in the trunk as it bypasses the smart battery monitor and can mess with the charging in future.

[HighlandPete]

Originally Posted by snowbimmer

My battery died a couple weeks ago. I was talking to my service guy about this very thing. The manual only talks about using another car to jump your BMW. He said it works fine the other direction too.

Personally I wouldn't use my BMW as the donor car. May be technically possible, as it is a two way connection, but knowing of a car's electronics being fried doing so, definitely act with caution.

If you do so, do everything you can, (all consumers off) to reduce risk of voltage spiking to electronics and ensure you follow the correct connection order, donor to assisted vehicle.

[Rono63]

Originally Posted by HighlandPete

Personally I wouldn't use my BMW as the donor car. May be technically possible, as it is a two way connection, but knowing of a car's electronics being fried doing so, definitely act with caution.

If you do so, do everything you can, (all consumers off) to reduce risk of voltage spiking to electronics and ensure you follow the correct connection order, donor to assisted vehicle.

I agree. Heard too many stories of people frying a control unit.

[Bc2005]

Sorry about the long post:☺️

In my experience, many folks don’t have experience in how to jump start a car, so there is potential for frustration (doesn’t work) and errors (hooked up wrong).

You really need to have two people with hands-on to work the problem.

- Each one holds the leads apart as the positive leads are connected, then the negative leads. Then double-check that the clamps are well connected and the jumper cables are supported so they won’t pop off from wire tension or vibration when the car starts.

Note- If you have an old towel or other material handy, use it to cover the dead battery. This should limit the damage if the dead battery is shorted or has some other defect that could cause it to explode when you attempt to charge it. Keep your face away from the battery as much as possible. Keep bystanders away.

- leave the “dead” car ignition off and start up the good car. Run the rpm up to about 3k for a few minutes so it is definitely charging both batteries. If the old battery was really dead, let it charge a little longer.

- now let donor car come back to idle and try to start the bad car. In many cases it will already have enough juice to start.

- If not then have one person raise the donor car rpm to about 3k and hold it, and attempt another start. This step can be difficult because many drivers aren’t used to hearing an engine at 3k rpm and they keep letting the rpm drop.
If you don’t get good strong cranking speed, then you need to recheck the cable connections because power is not getting to the bad battery connection. In most cases it will crank fast enough and immediately start.

- shut the donor car off. have both folks go back under the hood and pull the jumper cables off, first the negative terminals, followed by positive

My current solution is to just carry one of the rechargeable jump starter packs, because good quality/gauge jumper cables are bulky and there is no under-trunk storage in the G20. It probably won’t be enough for a really dead battery, but the jump pack is a simple solution for a car where someone just left the lights on too long in the parking lot.

[HighlandPete]

Originally Posted by Onesie

If you guys are going to perpetuate myths maybe you should post evidence instead of hearsay.

If you are talking about my post... I don't need to provide 'evidence' of my experience. No myths... simple experience.

BTW, I posted in the context of a warning and minimising risk, if you do use your BMW as a donor car.

BMW User Manuals are full of warnings, but users still mess up their vehicles.

[tturedraider]

Originally Posted by HighlandPete

Personally I wouldn't use my BMW as the donor car. May be technically possible, as it is a two way connection, but knowing of a car's electronics being fried doing so, definitely act with caution.

If you do so, do everything you can, (all consumers off) to reduce risk of voltage spiking to electronics and ensure you follow the correct connection order, donor to assisted vehicle.

I agree. I did it once with my E90 and it blew out my corona rings lighting. Too many electrical components to chance it.

[Chihuahua]

Originally Posted by Onesie

If you guys are going to perpetuate myths maybe you should post evidence instead of hearsay.

I’ve never heard of frying anything by jumping someone, unless people are making mistakes such as inverting polarity or touching both leads…

I’ve done it numerous times and will continue to.

Agree, have done it successfully many, many times over with many, many BMWs. I used to jump my neighbors work truck at least one per month with my E60. It's a car, it's not the freaking space shuttle FFS.

[Ximian]

Originally Posted by Onesie

I’ve never heard of frying anything by jumping someone, unless people are making mistakes such as inverting polarity or touching both leads…

I’ve done it numerous times and will continue to.

Those two mistakes that happen quite often? Some people are "helpful" and connect the cables to their dead battery *first* instead of the correct way.

I recommend a portable jump pack instead - it's safer and much quicker. You can get one for under $100 that has USB ports for charging devices and even an air compressor for inflating tires.

Personally, I'd use a battery tester on the receiving car to make sure it's not nearly dead. Batteries can explode and it's not pleasant, especially if your car is still connected to it.