How Effective It Is To Jump Start/Charge The Battery From The Front Terminal

[jim628]

Hello:

I haven't been driving my X5 for several weeks so last week the car could not be started because the battery is completely dead. I tried to jump start the car using the provided positive terminal on the engine compartment but it didn't work. When I turned the ignition key on to start the engine, there is still no electricity (no lights on the instrument cluster came on at all). Being panic for not able to jump start the car, I decided to look for the battery to try to jump start the car again directly from the battery terminal. (since this is my first BMW, I had a hard time finding the battery before I finally found it and I could not find this information in the manual either). This time it worked!. So here are my questions:

[1] Since my car is not driven very often, I decided to purchase BMW Advanced Charging System and keep it charged whenever I am not driving it. Since jump starting my car can only be effective if I do it directly on the battery itself, does this mean I have to connect my charger directly to the battery also?

[2] As a side question, I read so many comments that jump starting a modern car can ruin the control unit/processor. Now my car is normal when I drive it however did the jump start cause any damage?

[3] When I was shopping for my BMW Advanced Charging System I saw a fancy jumper cable that has resistor to prevent voltage spike. Anybody heard about it? Any recommendation where what brand and where to get it?

Thanks,
Jim

[JCL]

Front terminal worked just fine for me. Did you have a good connection on both cables at the front?

If you see no problems after jumping it, you didn't likely damage anything.

[WAYNE'S X5]

Mine jumped fine aswell as i left the tailgate open while carring out a repair under the hood (all day).never replace a vacum pipe from the manifolds yourself !

[jimbeattie]

I use the front terminals to jump start and charge the battery. No problems experienced yet. I believe the manual advises that you turn on air condidtioning fan and as much electrics as you can so that the boost doesn't damage anything.

To prevent the flat battery problem I use a solar panel plugged into the cigarette lighter socket.

[Eric Le Baron]

Regarding the instruction to switch on some high amp users before jumpstarting/charging car with a dead battery:

I have a cheap charger which produces about 17 Volts without load.
If it would be connected to a dead battery which has a high resistance value for some reason there would be way more then 12V on the car's electrical system if there's no high amp user switched on.
That might fry the car's (low amp) computer.

I have a more expensive microprocessor equipped charger as well and that one shows 0 V when not connected to a battery.
Looks like that one first looks at the load and then crancks up the voltage.
Not sure but wouldn't surprise me if it would never give more then just over 12V if it measures hardly any current with that voltage.

[X5Sport]

The advice I have just had from the dealer is to always disconnect the battery to charge it (and yes it is a pain to do - but safer for the on board electronics), and that the charger must have a 'low start' capability. This puts a lower amount of charge in to begin with (1-2A) and then builds it up to a level of up to 10A over a period of time. BMW batteries are not good a taking high current (booster chargers) without damaging the battery cells due to the high current causing heating and potential distortion to the plates in each cell.

The technician also recommended taking the battery out of the vehicle, turning it upside down and giving it a gentle shake. Something to do with allowing the magic eye indicator to work properly - it's a new one on me too!! Personally I would be extremely careful if choosing to follow that particular piece of advice.

He also recommended using a stand-alone vehicle battery as a "slave off" device, NEVER another vehicle as the other vehicle's charging system could cause damage, particularly once both engines are running and therefore two alternators are running in parallel.

[motordavid]

-I've had to jump mine, a couple times, way back in the car's youth;
both times it was done through the front under hood connections
with no problems. (That orig battery went on to live for 6+years and
59,000 miles, too.)
-Any good low amp trickle charger can/should be connected to the
front under hood connections, imo. The fancy BMW one and, some
Battery Tender versions, come with a plug for the cig lighter which
should alleviate having to use those front connections and certainly
not have to connect to battery in rear of car.
-I've never disconnected my X or Vette or motorcycles' batteries
when using my Battery Tender trickle charger...must be a UK thing.
-I left my X on the trickle charger via an appliance timer, for weekly
charging, in my unattended garage for 5 months and it worked like
a charm.

Yes, weird stuff can happen; save me the lectures...I've never had
a problem in low amp/sustained float/short, medium or, long term
charging.
GL,mD

[Mister2]

Worked fine for me

[Tomaz]

That's what BMW designed if for and it's the same as hooking it up to the battery.