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_3

boatman wrote: »

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_3

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

manda1205 wrote: »

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

tomstickland wrote: »

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.