CHARGING FLAT BATTERY - UNDER BONNET OR IN THE BOOT???

[shy7g]

Hi All
My X5 has sat for about 6-weeks now and although it had a new battery at the beginning of the year it's flat as a pancake. Can I recharge the battery from under the bonnet with the battery still connected or does it need to be done from the boot with the battery disconnected?
If from the boot does anyone know how to open the lower part of the tailgate?
Advice appreciated

[Chrisw4266]

When I worked for BMW we would charge them on the terminals under the bonnet while servicing/doing software downloads. Think you'll be ok but would recommend turning off the auto lights and auto wipers as these are powered up permanently.
Obviously don't put the ignition on whilst charging.

[X5Sport]

BMW recommend the under bonnet points.  A lot easier than digging into the boot, and less chance of accidentally firing the pyro squib that shears the main battery cable!

Richard

[AW8]

Under bonnet for sure.

Maybe worth a very experienced BMW Indy looking into what (if anything) may be draining the battery.

Final stage resistor a favourite as can be an old hard wired phone or module. 

[X5Sport]

6 weeks is not unexpected given the alarm etc is running.  Even Dealer cars have to be recharged monthly.

Richard

[AW8]

Hmm - I missed that bit  ::)

[kjb1]

I personally think you have a drain somewhere on the car.  If its a brand new battery, 6 weeks is very premature in my eyes.


Sent from my iPhone

[shy7g]

[quote="kjb1"]
I personally think you have a drain somewhere on the car.  If its a brand new battery, 6 weeks is very premature in my eyes.
Sent from my iPhone
[/quote]
Yeah fully agree but I think it's mainly due to it not being used, it may get used once, poss. twice a week if I get the time. I've been pondering for sometime now about letting her go, cause she just doesn't get out.
thanks for the info. ALL

[X5Sport]

[quote="kjb1"]
I personally think you have a drain somewhere on the car.  If its a brand new battery, 6 weeks is very premature in my eyes.
[/quote]

You have to factor in actual charge state when switched off, external temperature, normal current draw by the constantly powered systems as well as natural discharge rate.  The battery is not completely disconnected once the car is asleep, there are always systems powered and running.  The OPs battery is not brand new and in all likelihood was not 100% charged.

Even a fully charged, brand new battery will be showing signs after 6 weeks which is why BMW issued the TI to dealers telling them to charge cars every 4 weeks if not used.  Most of us may well have seen a Tech going round even showroom cars with a dharging unit as part of normal operations at a dealership.  These engines need a lot to crank them and the systems draw a lot of power when running. 

[Smeeagain]

If a battery isolator switch was fitted in the boot would that shut off the powered systems and would doing so cause any issue with those systems (other than there would be no alarm obvioulsy)

Smee

[X5Sport]

Other than killing the car completely - I can't think of anything obvious.  You will need one that can handle at least 900A for a diesel, or whatever the equivalent is for petrol engines.  If you go too low you may burn out the switch contacts when starting in cold weather.  I know they don't draw that much but you need to have a good margin and the diesel can easily exceed 800A momentarily, more with a dodgy starter.

The E53 has two +ve battery output cables.  One heavy for starting etc and main power distribution, which has an explosive cutter on it that activates in the event of an accident, and a thinner cable that keeps certain accessories (phone telematics as an example) running in the event of the same.

Richard