BMW e46 m3 (2002) battery/ alternator problem, HELP PLEASE

[1mm3]

Car: BMW e46 m3 (2002) 3.2l

1st day- car taken to Trafford centre, drove there fine. Would not start on return journey, clicking sound (lights getting dimmer over time, windows started slowly opening and closing electronic malfunction?). Jump started off another car after 5 min soak.

Left to charge overnight- started fine in morning got to work. After 8 hours (work) same thing but this time completely dead would stutter even unlocking car/ no lights or dashboard lights. Jump started after 5 mins no prob again.

Battery shows black (insufficient charge colour), checked by halfords (while connected in car, car off) was giving 12v and 96% starting power.

Took car to garage who checked car- removed negative terminal car stayed on etc they feel it was battery.

Battery is original OEM (9 years old?) Once the car has started there is no battery light (on dashboard). I'm unsure if battery/ alternator? Just don't want to spend £75 on a battery only to find it was the alternator afterall (another £200+ fitting).

Any other tests I can do to find the cause of the problem? Any help would be greatly appreciated.

 

[1mm3]

does the battery have 12v without alternator running? does that battery have 14v while the alternator is running?

I think that is what it is supposed to do.. however the guy at halfords did not check/ ask me to turn on car and check again. He just said "your battery is fine gents" (dad was with me).

Are these battery check tools cheap, i could just buy and check myself?

 

[1mm3]

Do you have the battery charge light on when driving?

If not its probably not the alternater. You may have an electrical fault that's draining the battery.

Common cause of this is the final stage resistor in the climate control. Had any issues with the climate?

When driving the battery charging light is OFF (there is no warning lights on the dashboard).

When the battery is left to charge, then disconnected after charging (overnight), when tried in next day it started up fine again (ie. battery is holding charge when left disconnected from car). Could be either alternator not charging battery when running/ something draining battery when switched off?

Ive never had any probs with the climate control neither- I have had problems with the horn in the past - it would randomly just start going off when im not pressing it- i replaced the fuse in the fusebox (using one from the middle row) and never had any problems since.

 

[1mm3]

If you're getting charging voltage (14-14.5v) with the engine running then you can be 99% sure its the battery only.

I will run the on-board computer test for battery voltage tomorrow (following below video) and let you guys know how I get on (it gives the battery voltage both when off/ when you start up)

 

[1mm3]

Ok, ran the voltage test:

12.4-12.5 everthing off
14.3-14.4 1000 rpm on
14.4-14.5 2000 rpm on

I assume that means alternator is ok. I also checked the negative cable from battery, connection was fine and no signs of corrosion.

The battery was left unconnected for over 24 hours and not charged, when connected today started up fine again? ie. battery is holding charge fine and only loses it when left connected?

I have a feeling [TW]Fox may be correct about the final stage resistor (aka FSU). A google reveals people have experienced battery drain overnight sometimes without any symptoms (probs with climate control).

If I remove the FSU and leave battery connected overnight this should tell me if it is definately this/ battery alone?

Thanks again to all that have replied- the reason im being so cautious about walking out buying battery is ive personally/ seen online how lots of people have ran out and bought (in this case) replacement battery/ alternator/ voltage regulator only to find it was something else causing the problem.

 

[1mm3]

Do you have sat nav out of interest?

Removing the FSU and leaving the car overnight should work (assuming it starts in the morning).

Somethings to note about car batterys though, if it's been flat, and jumped / bumped a few times, the battery won't be in the best condition anyway. It takes, on average, 20 minutues of driving to regain the charge lost from starting a car. This time of year too (although, not that cold), even one dropped cell can render a battery inoperative and would need replacing.

No sat nav.

I have to admit i have a bad habit of switching the car off whilst the cd player is still playing/ fan on/ heated seats on. I find when i switch the car on- the fan comes on automatically/ cd comes on straight away too (Ive always assumed car keeps this in memory from last shutdown and nothing to worry about?)

I will probably remove FSU tomorrow and leave battery connected to see what happens/ try a battery isolator?