[northX3]

Hello !

Why is it recommended to jump start the car (ex in case of a drained battery) under the hood and not directly at the battery in the trunk ?

I did jump started the car this morning directly on the battery, and the car ran normally after that... Did I get lucky ?

By the way, my trickle charger is connected directly to the battery terminals at the back, should I reconnect the at the front ?

I thought the red and black poles under the hood were provided by BMW for "convenience" and traditionalism, but some other electrical threads here scare me !!!

[fiddy yen]

Originally Posted by northX3

Hello !

Why is it recommended to jump start the car (ex in case of a drained battery) under the hood and not directly at the battery in the trunk ?

I did jump started the car this morning directly on the battery, and the car ran normally after that... Did I get lucky ?

By the way, my trickle charger is connected directly to the battery terminals at the back, should I reconnect the at the front ?

I thought the red and black poles under the hood were provided by BMW for "convenience" and traditionalism, but some other electrical threads here scare me !!!

I Don't see it being an issue, however all the wiring is back there and the points in the front are there for convenience and safety (wiring etc). Question that I have is who installed your trickle charger in the back? Do you plug it in from the back too? or does it run all the way up to the front? Seems like a lot of wiring.

Who is your dealer if you don't mind me asking?

[Steve30dMSport]

Firstly, you should not connect jumper leads to both battery terminals at any time if the battery is in the car. You can connect them to the corresponding red terminals but the black earth connections should always be connected to an earthed metallic component of the vehicle itself; NOT the earth terminals of the battery. By using the specified terminals in the engine compartment you are abiding by this rule. The risk of connecting the jumpers to the battery itself (pos and neg) are the possibility of fire from sparks caused by accidental incorrect polarity or even damage to various ancillary components of the electrical system which can be very expensive to repair or replace.

Regarding the trickle charger, it depends on what you are using. I have a special trickle charger for the Porsche which plugs in to the power socket in the centre console and operates with the battery in the car, however, usually it is recommended to have the battery removed from the vehicle if recharging with a normal battery charger. I don't know what charger you are using so I can't really comment on your circumstance. I suggest you contact the service department of your BMW dealership and speak with them.

[paul386]

I would also advice to use the connection up front. Going through the battery in the back means your are passing high current though a much longer distance of wiring meaning a voltage drop. Voltage drop when you are having issues with starting the engine doesn't really help the situation.

By the way - I hate electricity.

[Steve30dMSport]

Originally Posted by Lotus7

You are correct in assuming that the terminals under the hood are there for convenience. They are certainly easier to access than the battery itself since you don't have to raise the cargo area floor.

The other issue is the emergency disconnect assembly on top of the battery (the large red plastic assembly). It's a remotely triggered "kill switch" and covers the positive terminal of the battery. An improperly applied connection to the Emergency disconnect unit will trigger it, requiring replacement. Finally, there is always the issue of hydrogen gas build up near the battery. This should not normally happen with the OEM BMW deep cycle saturated mat battery, but the possibility exists, so BMW doesn't want anyone generating possible sparks near the battery.

If your charger connections or jumper connections are directly to the battery terminals (especially the positive one) there should be no problem. However if you are accessing the positive terminal through (after) the Emergency Disconnect module, you may be risking inadvertently triggering it which will, of course, render the car undriveable until it's replaced. Using the front terminals eliminates this potential problem. Accidentally reversing the polarity by connecting a jumper battery improperly is a disaster if you do it directly at the battery OR at the front, under-hood terminals.

Wow, it must be awesome to be Lotus7.......

[Dr Stig 2]

Originally Posted by Steve30dMSport

Wow, it must be awesome to be Lotus7.......

Ahn Padowan, you too may learn the secrets of the Force.

[northX3]

Originally Posted by Steve30dMSport

Firstly, you should not connect jumper leads to both battery terminals at any time if the battery is in the car. You can connect them to the corresponding red terminals but the black earth connections should always be connected to an earthed metallic component of the vehicle itself; NOT the earth terminals of the battery. By using the specified terminals in the engine compartment you are abiding by this rule. The risk of connecting the jumpers to the battery itself (pos and neg) are the possibility of fire from sparks caused by accidental incorrect polarity or even damage to various ancillary components of the electrical system which can be very expensive to repair or replace.

Regarding the trickle charger, it depends on what you are using. I have a special trickle charger for the Porsche which plugs in to the power socket in the centre console and operates with the battery in the car, however, usually it is recommended to have the battery removed from the vehicle if recharging with a normal battery charger. I don't know what charger you are using so I can't really comment on your circumstance. I suggest you contact the service department of your BMW dealership and speak with them.

Thanks everybody for the kind answers.

I thought that there would be spark and gas explosion with jumper leads on the + and - poles of the battery because of the kind of battery BMW uses (less gas surrounding the battery compared to "old school" car batteries ?)

Here is the pic of my trickle charger. I did plug it on the battery negative pole, and on one of the terminal of the battery. Is it risky this way ? I tried the setup and it works well, but maybe I'm lucky and a disaster is waiting ?

PS : as a side note, I asked on the phone a BMW tech at my local stealership. They do install such trickle chargers like I did under the trunk floor, only leaving a quick-connect in sight, but he could not specify me which battery poles he was using...

[northX3]

Oh, I forgot.

I plugged my aftermarket amp and DSP at the same battery terminal points... everything worked well (until temperature went to 0F and I drove 2x10 minutes every 2 days with the X3, leading to the battery discharge !)

PS : if you wonder why I drove the X3 so few miles the last week, here is the answer

[walendvay]

You guys are missing something....

The terminals under the hood are located there by design. This point is electrically closer to the starter and it is a lower resistance path to the starter! When jumping the car, I suggest using them.

V= I*R. If jumping a car, you want as low of R as possible, otherwise V will drop and you will have less success in jumping your car!

Invest in heavy duty 10 or 8 gauge or less jumper cables. The lower gauge (thicker wire) the better! Be sure to verify the alligator connectors have a solid connection to the wire on the jumper cables.

For charging, the current capability of the charger will overcome the added resistance and the added R will be a moot point. Charge up front! This way, you don't have to clear your trunk!

I have had great success with a battery tender from deltran. Best price is on amazon. This is the same charger as the BMW labeled charger but less expensive!

Good luck!

[paul386]

Originally Posted by walendvay

You guys are missing something....

The terminals under the hood are located there by design. This point is electrically closer to the starter and it is a lower resistance path to the starter! When jumping the car, I suggest using them.

V= I*R. If jumping a car, you want as low of R as possible, otherwise V will drop and you will have less success in jumping your car!

Invest in heavy duty 10 or 8 gauge or less jumper cables. The lower gauge (thicker wire) the better! Be sure to verify the alligator connectors have a solid connection to the wire on the jumper cables.

For charging, the current capability of the charger will overcome the added resistance and the added R will be a moot point. Charge up front! This way, you don't have to clear your trunk!

I have had great success with a battery tender from deltran. Best price is on amazon. This is the same charger as the BMW labeled charger but less expensive!

Good luck!

Not this guy...

Originally Posted by paul386

I would also advice to use the connection up front. Going through the battery in the back means your are passing high current though a much longer distance of wiring meaning a voltage drop. Voltage drop when you are having issues with starting the engine doesn't really help the situation.

By the way - I hate electricity.

[Ant Man]

I assume the owner's manual recommends charging the battery from under the bonnet?

Btw, does the X3 have IBS, meaning those plug-in chargers (to cigarette sockets / power sockets) don't work?

[northX3]

Originally Posted by walendvay

You guys are missing something....

The terminals under the hood are located there by design. This point is electrically closer to the starter and it is a lower resistance path to the starter! When jumping the car, I suggest using them.

V= I*R. If jumping a car, you want as low of R as possible, otherwise V will drop and you will have less success in jumping your car!

Invest in heavy duty 10 or 8 gauge or less jumper cables. The lower gauge (thicker wire) the better! Be sure to verify the alligator connectors have a solid connection to the wire on the jumper cables.

For charging, the current capability of the charger will overcome the added resistance and the added R will be a moot point. Charge up front! This way, you don't have to clear your trunk!

I have had great success with a battery tender from deltran. Best price is on amazon. This is the same charger as the BMW labeled charger but less expensive!

Good luck!

Good point ! Lotus also has a good point ! I think we're splitting hair on this one

I used the battery terminals in the trunk for a hidden install... it was easier to bolt the battery charger's round connectors to the battery posts than to the terminals under the hood.

If someone's interested, I will upload pics of the final, stealthy install.


I should move farther away from my job, so I would have to drive more than 5 minutes to get there ! Or move to somewhere where the temperature is hotter than 0F in the winter ! Or ditch the 2nd daily driver I use !


PS : Lotus, the NSX is great so far. Don't know yet about rear tire life, it's a trade-off for the rear geometry and grip, I guess... The later NSX had better tire mileage with an adjusted rear geometry and alignment specs, though. I'd love to own a Super 7, but the wife isn't so sure about the helmet wearing on Sunday rides, so the Acura was the "family choice"