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Flat Battery JUMP LEADS or RECHARGE

BMW forum 5 series car: E12, E28, E34, E39, E60, E61, F07, F10, F11

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Flat Battery JUMP LEADS or RECHARGE

Postby shafire » Tue, 08 Jan 2008 22:56:09 UTC

hello all

my e39 528 sport has a flat battery due to not been used for about 7 weeks NOT my choice gutted. :evil:

Anyway was thinking of using Jump leads from my diesel van etc or one of these booster battery things you can get now,
but heard of people in the past Damaging the ecu due to a surge charge etc, since these have a Higher amperage etc. :roll:

Has anyone had a problem?

was thinking of taking it off and recharging it since it seems the less likely to cause any problems or does this
effect the alarm once installed again i take it there's no radio code on these BMW? :roll:

Ta Rob
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Postby baboo pardesi » Tue, 08 Jan 2008 23:51:41 UTC

It's a myth you will not damage the ecu if you use the jump leads start method..
Some BMW 's do have the code older ones I know did.. but the E39 is code less..
Last edited by baboo pardesi on Thu, 10 Jan 2008 00:22:31 UTC, edited 1 time in total.
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Postby thomp1983 » Wed, 09 Jan 2008 00:07:55 UTC

it's not a myth about voltage spikes damaging car ecu's but all you need to do is leave the car connected to the jump leads for a couple of minutes at idle after it's started to allow the voltage to level out

chris
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Postby phelix » Wed, 09 Jan 2008 08:20:13 UTC

If possible run the "donor" car's engine for a few minutes with the leads connected to start the charge of the dead battery.

It's a good idea to turn off the donor car's engine when trying to start the car with the dead battery but the voltage drop across the jump leads and resulting voltage at the dead battery may mean there's not enough juice to start the car. The reason for doing this is that when the engine of the donor car is running the alternator will greatly increase its output while the dead car is cranking over. That high load will suddenly disappear when the dead car starts which *may* result in a voltage spike before the voltage regulator can respond. Having said this I follow my own advice about 50% of the time and have never had a problem either way!

Those booster packs that you can buy for £20-30 are quite useful to have around for starting cars with flat batteries and as a general 12V power supply. Some have a small air cmpressor built in.
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Postby jon-willy » Wed, 09 Jan 2008 08:52:26 UTC

phelix wrote:Those booster packs that you can buy for £20-30 are quite useful to have around for starting cars with flat batteries and as a general 12V power supply. Some have a small air cmpressor built in.


And a coffee machine.. :wink:

Seriously you cannot beat a good overnight charge, starting from jumper leads will certainly get you away but unless you are going to travel a hundred mile or so the battery will not get to a full charge and could/will lead to you being let down again.

About five years appears to be the reliable life of batteries from what I have noticed on the forum, after that you may be pushing your luck.

Its also fair to say you can expect the battery to run down after being stood that length of time, its recommended to either use a trickle charger or disconnect the battery if you know it will be stood for any great length of time.

Jon.
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Postby ajbsmirnoff » Wed, 09 Jan 2008 11:50:10 UTC

buy a charger and leave it overnight.
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Postby shafire » Thu, 10 Jan 2008 23:32:42 UTC

Thanks Lads for the advice

I'm going to play safe and remove the battery and charge it overnight.

ROB
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Postby machinehead525 » Fri, 11 Jan 2008 20:21:17 UTC

I've had the RAC jump mine, all be it an E34, and they ran the jump leads to the car for at least 5 mins, if not 10, before even trying to start my car giving the battery a well needed boost. All was fine. A good charge over night would be preferable I'm sure! I would avoid just a jump start personally but I'm not a tech guy so its opinion not fact.............
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Postby manowar » Fri, 11 Jan 2008 21:33:23 UTC

I'm going to be a bit more careful now. I'm always jump starting my 5's, just connecting up, starting up and disconnecting, never really given jump starting much thought as I haven't needed to in my previous cars. Usually I have to jump start because I've accidentally had the stereo on too long between starts whilst I've been cleaning or working on the car. My 523's probably had about 10 jumps in my ownership and my 530 probably about 3. As of yet I've had had absolutely no problems at all, though I'll count myself lucky and heed this good advice!
It's not leaking oil, it's sweating power...
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Postby redfazer » Fri, 18 Jan 2008 00:57:20 UTC

You do not have to remove the battery to charge it up - there are two terminals beneath the bonnet (well there is on my touring anyway).

I give my battery a charge every weekend in the winter - what with the lights, wipers, heater demister etc always being on.
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