Flat Battery - BMW 316

[BombJack]

Ok - I made a booboo last night. Parked up the car, only to find this morning that I had left the headlights on all night - flat battery.

So, my girlfriend phones up her old man so he can maybe do a jump start.
Thing is though, he's heard horror stories about onboard computers and stuff frying as a result of doing this with BMWs.

So, can anyone tell me what we should do? We don't really want a huge garage bill to get this sorted.

Anyone got any tips?

ps sorry mods if this is in the wrong place btw...

[vikingaero]

I've jump started loads of modern cars without frying anything. Make sure the radio, lights, fan etc are off.

Leads go:

Red + on healthy car to Red + on flat car
Black - on heathly car to an earth point such as the engine lifting point

Wait a few minutes. Then start the car. Sometimes if I know that the flat car is as flat as a pancake I'll start the healthy car for extra juice.

[boatman]

Saw in the car auctions when using their battery start pack they turned on the fan and lights. The thinking was that any surge would be taken by them not the electronics. Why not bump start it?

[Conor]

Saw in the car auctions when using their battery start pack they turned on the fan and lights. The thinking was that any surge would be taken by them not the electronics. Why not bump start it?

Because it won't work if the battery is completely flat as there's no voltage there to create the field in the alternator so you just tow it round endlessly with nothing happening. Alternators need a small amount of current available to work.

So when you see people trying to bump start cars for ages, that's why it doesn't work.

[anewman]

Other option is a £10 car battery charger overnight from wilkinsons.

[Conor]

Or one of those portable booster starter packs but not the pathetic things that plug into the lighter socket - a proper one with decent leads that connect directly to the battery.

[tomstickland]

I've never had any problems with jump leads. How do the components know any difference from the normal battery and the jump leaded battery?

[manda1205]

the auction uses jumper packs (propper 1's that cost thousands) because its not very professional to push start all these cars and things can break if you do (hands pushing lamps and spoilers etc)

if the battery had a internal fault (left on a car for years untouched) then it may not push start cos the battery is no longer making a circuit but if its a servicable battery it'll start with a push fine, soon as the lumps turning over it'll sort the ignition with power and off she goes, longer pushes needed for efi

as for jump starting frying ecu's its balls, ive heard these stories for years and its never from any1 it ever happened to, jumping is the same as normal starting, managment is protected from such problems by alsorts of jiggery pokery

i pref a good car battery for jumping and some really good jumper cables, a crap battery and wilco jumper cables wont start a moped and jumper packs under a few hundred quid are not worth the space they take up

if you do it alot a lorry battery will start anything, just dont forget to turn your lights off and if you do, beg/borrow some jumper cables from somebody whos handy and off you go again

[anewman]

i pref a good car battery for jumping and some really good jumper cables, a crap battery and wilco jumper cables wont start a moped and jumper packs under a few hundred quid are not worth the space they take up

The benefit of the Wilkinson's cheapo battery charger is that it trickle charges. Argos sells more expensive ones that will super fast charge your battery in half an hour or something silly like that, but they may potentially damage the battery reducing it's ability to hold charge in future.

I would personally not bother with the jump packs at all as all they do is sit in the garage for years on end and someday that battery in there is going to pack in due to not being used at all. Don't know if this applies to the pro equipment costing a few hundred, but my guess is they're designed to be used rather than kept in the garage.

If you make sure any beep mechanism working designed to warn you of headlights remaining on when the door is opened, will help prevent it again :)

[tomstickland]

I've never had any success with battery chargers. The alternator should charge the battery whilst the car is driven anyway. I've found that once a battery loses charge once then it'll do it again. ie: they're usually knackared by that time, so I replace battery with another one from motor factors.

[espresso]

How do the components know any difference from the normal battery and the jump leaded battery?

They don't but a voltage spike can be induced momentarily when the jump leads are connected and disconnected which can damage some electronic control circuits, which is why some people recommend having the lights on as per post #3.

[BombJack]

the auction uses jumper packs (propper 1's that cost thousands) because its not very professional to push start all these cars and things can break if you do (hands pushing lamps and spoilers etc)

if the battery had a internal fault (left on a car for years untouched) then it may not push start cos the battery is no longer making a circuit but if its a servicable battery it'll start with a push fine, soon as the lumps turning over it'll sort the ignition with power and off she goes, longer pushes needed for efi

as for jump starting frying ecu's its balls, ive heard these stories for years and its never from any1 it ever happened to, jumping is the same as normal starting, managment is protected from such problems by alsorts of jiggery pokery

i pref a good car battery for jumping and some really good jumper cables, a crap battery and wilco jumper cables wont start a moped and jumper packs under a few hundred quid are not worth the space they take up

if you do it alot a lorry battery will start anything, just dont forget to turn your lights off and if you do, beg/borrow some jumper cables from somebody whos handy and off you go again

Ok here's the deal. With respect to frying the electrics, it is possible if you are trying to jump a BMW with a car that uses a different voltage ie Ford, or Vauxhall. the reason being, that BMW use a 12.6 volt system, whereas the Fords use a 14.5 volt system.

It turns out that there shouldn't be a problem as long as the car providing the charge isn't actually ticking over, ie engine running. this would provide to much of a charge and potentially fry the BMW's electrics.

We did try to bump start it, but as a previous poster mentioned, if the battery is completely flat it won't matter how much you try, the engine won't kick in.

Interestingly, we got a neighbour to come round with his leads to provide the initial jump, which appeared to be ok - ie we could start our car. Thing is, as soon as he released the jump leads, the engine would die.

Why is this? Any ideas?

[tomstickland]

It suggests a totally knackered battery or a wiring fault.

[espresso]

Ok here's the deal. With respect to frying the electrics, it is possible if you are trying to jump a BMW with a car that uses a different voltage ie Ford, or Vauxhall. the reason being, that BMW use a 12.6 volt system, whereas the Fords use a 14.5 volt system.



Sorry but that is rubbish as they both use 12V batteries. The output from the alternator may reach 14.5V on both makes of car but the batteries are 12V.

Sounds like you didn't give the battery long enough to take some charge, before disconnecting the donor battery if the engine died. You can't charge a battery in minutes if it is totally flat.

[manda1205]

It turns out that there shouldn't be a problem as long as the car providing the charge isn't actually ticking over, ie engine running. this would provide to much of a charge and potentially fry the BMW's electrics.

Surely if you do that you're just taking the donor cars battery power, then gonna leave that one flat, sorry if thats an ignorant thing to say but I thought it had to be running to keep the alternator charging the donor cars battery????? And also agree with above posts, gotta leave it running for a while to give it enough power otherwise it will die(and also going on a long enough run to charge the battery (and turn your radio/lights off)otherwise when you stop again its gonna be flat again), and if you did this then go buy another battery.

[misterthrifty]

Hi

Interesting reading as my car had a flat battery today, and I only fitted it a month ago. The breakdown bloke says there could be an intermittent problem with the battery being drained. I thought about getting a booster pack just as a back up, are they really no good or do they at least work in an emergency?

[Conor]

Ok here's the deal. With respect to frying the electrics, it is possible if you are trying to jump a BMW with a car that uses a different voltage ie Ford, or Vauxhall. the reason being, that BMW use a 12.6 volt system, whereas the Fords use a 14.5 volt system.


Utter tosh.

Measure the voltage across the Ford when it's not running and it'll be around 12.6V. Measure it with the engine running, it'll be around 14V. Likewise the BMW.

[Conor]

Interestingly, we got a neighbour to come round with his leads to provide the initial jump, which appeared to be ok - ie we could start our car. Thing is, as soon as he released the jump leads, the engine would die.

Why is this? Any ideas?

Alternator is knackered and the battery is so flat it can't keep the engine running.

[manda1205]

ha ha ha, all 12v systems shoudl charge at 14v or a little above


if the car runs while jumped leave it for 5 mins to get some poke in the flat battery, then disconnect the jumpleads, if it still cuts out battery is dead, if it keeps goin for a bit then dies alts not charging, battery could be on its way wount neways if it goes flat over time and if didnt before (if it did before there could be a rain on it like a constantly powered stereo or faulty switch holding something on)