[gchild]

Bought a used e90 55 plate 325i from a trader last week. 34k on clock and full history confirmed by BMW. Idrive elec seats etc. Paid top whack as it was like new!

Since then the car has failed to start and needed to be jumped so I put it down to the battery never being replaced and changed it yesterday. All good for rest of day, but again left overnight and failed to start again this morning.

Sounds like a battery drain somewhere which could be anything.

Are there any common issues like this that are easy to fix? If not I will be pushing the trader to take the car back which would be easier said than done.

Advice appreciated as this is souring my first experience of BMW ownership

[creepy coupe]

Assuming the new battery had a decent charge, then for something to drain it overnight, it must be something drawing a reasonable load. I'd start with the start side of things. Recharge the battery and disconnect the heavy power cable to the starter motor.

Still worth checking the boot lights are switching off though.

[gchild]

I did a 12 mile round trip in it after fitting so should've got charged up if the new one was low. No warnings at all on dash.

Does the boot light switch off once closed or is there an override? Not sure how it can be checked with boot closed.

Am I doing something silly with the start procedure? Stick key on, foot on brake and press start button? Cat is in park. I did the exact same process when jumping it and it would start which rules out a dodgy start button.

[xenon]

The starting procedure is correct but the current drain must be fairly significant. Boot lights isn't a bad shout but even then it shouldn't drain a healthy battery overnight. Easy check though - take the bulb out.

[m1bjr]

I drive will ping you when the voltage is low - its very obvious.
Are you getting the low battery voltage alert?

What I'm getting at - are you sure the battery has drained, or it it a starter motor issue?

There is no issue I know of specific to these cars, but only a generic fault find.
Easy test is to meter the current drain, any auto electrician can do this quickly and cheaply.
Try a mobile service like the AA/RAC - you have cover?

Tech- there are heaps of stuff that run on these cars without you being present.
I would attempt the easy fix first, battery completely disconnected for an hour to eliminate possible software issue holding on the ECU power or something.

[gchild]

No alerts or pings

If it starts when jumped the ok after a run, this should rule out the starter motor?

When on time came out, they checked the alternator and said it was fine. Also the little green indicator was fine on the old battery.

[gchild]

I will disconnect the neg terminal tonight to check the Ecu memory thjng mentioned.

[xenon]

I'd be removing the boot bulbs first.

[confused.com]

Get the AA out mate, they have a device that checks various things for power drain, really good tool.

P.S Take the battery back to wherever you got it, they'll replace it. Had an issue with my e30 325 where it drained the battery every 3 months or so - Europarts happily replaced each time 'sorry sir, seems to be a faulty battery'! I had 4 batterys in total.

[gchild]

Originally Posted by xenon

I'd be removing the boot bulbs first.

i will try this too. i assume in your experience this could be a very really reason for the drain...if it turns out to be this, is it the boot switch that needs to be replaced?

[gchild]

If the lights aere left on the 'auto' switch, could this be a cause of the drain? no lights appear to be externally on when leaving the car, so a long shot. That is the only thing i can think of without yet trying any of the above suggestions.

Also, just rang the trader, he said they had no issues with the car while it was with them on their forecourt as they were moving it inside daily to ensure no oen nikced the wheels. They are happy to look at it, but strongly implied i must be leaving something on

I can't think of anything i've changed? radio, lights etc all go off when switching off the car.....

[magic77]

Just a side note I recall reading somewhere when changing the battery the e9x had to be coded to tell it there is a new battery.

[gchild]

I've read that too, but found no evidence of this step in the manual

[m1bjr]

Originally Posted by gchild

I've read that too, but found no evidence of this step in the manual

Red herring.

Only applicable if you have fitted a different capacity really.
The DME uses the figures to accurately calculate battery run time and the warnings I mentioned.
And the charge rates etc.

If I leave the ignition and lights on in mine for a half hour then I generally get the low battery alarm.

You are not. Which makes me wonder if the battery really is flat.
Or perhaps the starter is drawing excess current/failing.

You did fit EXACTLY the right size and cranking amp rated battery ???

[foxy-stoat]

you have a volt meter on the hidden menus which will tell you how its charging.

not sure the numbers tho...search hidden menu wetpaint for the full list

[edowen]

Stupid question, but have you told the dealer you bought it off, and asked him to investigate it?

[m1bjr]

Originally Posted by edowen

Stupid question, but have you told the dealer you bought it off, and asked him to investigate it?

LOL - I would have got it delivered straight back there myself.
Perhaps its very remote, or there is no alternate transport.

[foxy-stoat]

Originally Posted by edowen

Stupid question, but have you told the dealer you bought it off, and asked him to investigate it?

Post #11 says he did.

He needs to give the dealer a chance to fix before he can reject the car.

An auto electrican will be able to pin point the drain quite easy. Had an mr2 hat used to drain the battery over night and that was the boot light.

[gchild]

It's not from a main dealer but the company I bought from has been told.

The new bosche battery is slightly better spec than the oem one. 74ah vs 70ah and higher cranking charge

[m1bjr]

Originally Posted by gchild

It's not from a main dealer but the company I bought from has been told.

The new bosche battery is slightly better spec than the oem one. 74ah vs 70ah and higher cranking charge

So you need it coding to the car.

[gchild]

But would that cause the drain after less than 12hrs? Plus the same symptoms on the oem battery before removing it.

Who can code it and likely cost?

[gchild]

trader has fixed the car and awaiting collection. turns out the 'battery amplifier' was faulty and draining the battery within 3hrs. Part replaced and issue resolved.

A common issued according to him... i didn't find anything on this forum, nor heard of a 'battery amplifier' before. Thoughts?