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Cooper S Battery Drain Issue

49K views 21 replies 11 participants last post by  casper911ca 
#1 ·
Hi all, long time since I've been on here.

Anyway, I'll cut to the chase, my 2002 Cooper S battery was rather old so I replaced it last August. Up until December I could leave the car for almost a week and it would start straight up. But now since Christmas if I leave it for over a day, it dies and needs to be jumped in order to start it :(

I've charged the battery up, had a multimeter on it and it shows between 12.6V and 12.75V and when I start the car I get around 13.7V to 14.2V, so I'm happy that the alternator is charging the battery.

So this leads me onto the thinking I have a spurious drain on the battery. I've not installed anything new in the car for a long time, so that can't be it, which means I'm going to need to test for the drain.

My issue is that with the battery located in the boot, I'm not sure what the best way is to do this, because if I'm going to have to start pulling fuses, it'll be a lot of running around. Is there a way to block the door/boot sensors to stop the car from thinking the door/boot is open?

Are there any common issues that I could look at first to maybe locate the fault? Is it likely that the fault could be stored in the ECU and a simple OBD reader could diagnose the issue for me?

Thanks in advanced for some help.
 
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#2 ·
Hi an obd sensor might be able to diagnose it but it definitely will not fix it.

i also for it to be that sudden after a battery change, it is unlikely but the new battery could be duff.

try testing the battery when you get home
and when you get to bed if the volts drop dramatically then you either have a duff battery or a significant power drain::frown::

i would also get your local mechanic to do a battery load test this will show if the battery is faulty.
and he might be able to diagnose the possible power drain:nerd:
 
#3 ·
Thanks for your response, that's what I meant by using an OBD sensor, if it could possibly identify the fault then it's worth a try :)

I took the car to kwik-fit for their free battery test (I know they use a really good Bosch tester thing), they came back and said the battery and charging circuits are fine, which leads me onto believing it's a parasitic draw on the circuit :-(

After using the car most of the weekend (definitely last night), and it pouring down with rain, I'm suspecting there may be water getting in somewhere shorting something out. As I understand it, this can cause a power drain issue (unless I'm talking absolute rubbish).
 
#4 ·
Check all your Earth cables and get it up on jack stands and make sure there are no abraded cables against the bodywork etc. Don't forget your ECU is always drawing power (minimal) from the battery so you will always have a parasitic draw. You should be able to leave it longer than a week at least before it starts to get low but are you also in a very cold temp area as that may not help in keeping it healthy. If your going to let it stand, disconnect the Earth to the Battery and if its exceptionally cold at night, store it in a warmer environment and give it a 24hr trickle charge before you intend to use it (either get a smart charger or trickle charge it every 2 weeks when stored).

When they said the battery is fine, did they test its CCA capability ?
 
#5 ·
I agree that there is always a little bit of a draw on the battery when the car is locked up for the night, but this is what I need to test, just unsure how to since things start to wake up the moment you unlock it and open doors/boot - This doesn't give an accurate reading.
Is there a resource that shows the main earth points to check?
I'm in the UK, so it's not really cold, just wet :p
Unfortunately, I live in a flat and don't have a garage, so the car has to be parked outside, this also makes it rather difficult to stick a trickle/maintenance charger onto the battery to keep it topped up.

The printout they have me listed 3 tests:-
Battery Test - Came back as good but needs a recharge
Starter System - Came back as cranking normal
Charging System - Came back as no problems

On that basis, I believe that means they did test the CCA capability (I could be wrong though).
 
#6 ·
There is an assumption that the CCA would be part of the battery test but it wouldn't hurt to check with them or have it rechecked for its CCA capacity.

Starter system just means it cranks over.

Charging system just means the alternator is doing its job.

The fact that it needs a recharge says that there is either a drain or an inability to hold a charge and provide the required CCA.

Take it out of the car and trickle charge it in the laundry, that way, if it vents (shouldn't be an issue unless there is a major fault with the battery whilst on trickle charge) its only a small room it cant do much harm.

There are numerous earth points on the car to check but I would be looking (from experience) any wiring from the starter motor etc that wasn't tied off correctly and has rubbed against a component. Check the power cable under the bonnet where the jumpstart terminal is and trace it down under the firewall and between the gearbox before it traces backwards to the boot.
 
#11 ·
Well, 4 months after changing it :p
Unfortunately, I disposed of the old one after replacing it (nowhere to store it and it was about 10 years old).

I fully accept that reasoning, it just (to me) doesn't make sense how it would be fine for ages and then suddenly die, I would have expected it to be like that from the offset - but then again, I'm not an expert :p
 
#14 ·
...My issue is that with the battery located in the boot, I'm not sure what the best way is to do this, because if I'm going to have to start pulling fuses, it'll be a lot of running around. Is there a way to block the door/boot sensors to stop the car from thinking the door/boot is open?
This is what I did in a similar situation - although you do need a multimeter that measures current -say up to 10A - nice autoranging one here for £10 via Amazon

With ignition off & doors shut behind you and having waited say 10 mins for all systems to shut down, remove each fuse in turn & measure for any drawn current across the 2 terminals.
Given your description of an almost complete battery drain over 24 hours, I'd expect the faulty circuit to be taking at least 1 amp.
Although best to note any drain from all circuits & then narrow it down.

On my old 2001 MINI it turned out that the radio unit was taking around 5 amps when off for no apparent reason - new unit & problem solved.
::smile::
 
#15 ·
With ignition off & doors shut behind you and having waited say 10 mins for all systems to shut down, remove each fuse in turn & measure for any drawn current across the 2 terminals.
Given your description of an almost complete battery drain over 24 hours, I'd expect the faulty circuit to be taking at least 1 amp.
Although best to note any drain from all circuits & then narrow it down.
Good advice.

Multimeter is far more versatile in the long term (especially if you learn how to use it) but one of THESE looks quite handy in that situation and if its anything like the 2nd gen fuse box I'd recommend a FUSE PULLER
 
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#16 ·
Thanks all, I do already have a 10A rated multimeter, so just need the time to troubleshoot this now.
Something I have noticed, at times using my jump pack to start the car, it just won't start from the boost points under the bonnet, instead I have to jump it instead directly at the battery. Could this sound like a dodgy/corroded earth?
 
#18 ·
You can get those PLUG IN TRICKLE CHARGERS for about £12 on e/bay (SOLAR POWERED) just place it on your back shelf.They are fitted with a one way thingamejig so when it gets dark it doesn't work in reverse (drain batt).
I've had one on a V8 Chevy truck middle of winter and all my other yanks..THEY DO WORK GOOD LUCK
 
#22 · (Edited)
Amp clamp is the way to go
They measure up to 400 amps
Trouble with cheap ones is you can blow them when putting them between terminal and battery as they are limited.

Sent from my SM-G900F using Tapatalk
Doesn't this only work for AC current? I just used an alligator clip on the positive cable out my DMM in current mode and pulled fuses one by one. With everything connected, all doors closed, my battery draws 0.5 A. Which is like 6 watts. Online research seems to suggest a Type 47 battery should be around 50-60Ah new, so that's like 100-120 hours with a 0.5A draw, that's like 5 days. After I pulled every fuse individually I found there wasn't just one circuit pulling all the power, it was a combination on fuse 4, Fuse 21 and fuse 24, each drawing about 0.1-0.2 amps a piece (Bentley manual says these are "General Module 1 (BC1)", "Instruments", and "EWS; alarm siren; ultrasonic sensor"). When I pull all three, the current draw drops to 0.04ADC (table below)

F20 is the fuel pump, I don't know why that one jumps and fluctuates, guessing there's some capacitance somewhere or the system tries to pressurize but it can't so it keeps trying (I never put the key in, so that doesn't make sense to me).

I pulled the whole bus plug on the fuse box under the hood and the current draw only dropped to like 0.47, very little difference. And by the way, you have to wait a few seconds while measuring the current because something runs (I think something in the instrument display, when you complete the battery circuit) for a few seconds drawing about 1/10 of an amp before the system settles to steady state.

According to the Bentley Manual, BC1 is a "sophisticated centralized design for body electronics which is self diagnostic..." According to the same manual (p. 400-6) it controls the wipers and washers, central locking and anti-theft, keyless entry, door windows, interior lighting, alarm system, sunroof, convertible top, seat memory, and rear-view mirror control and heating. It says BC1 Diagnostic Trouble Codes are accessible through OBD II.

Update:
I measured the current at the fuses after pulling each one, and fuse 21 (instrument cluster) is pulling like 0.22 amps. The other two are about 0.03A and 0.08 amps. I think there might be something going on with the instrument cluster.

Update 2: I did a Google search for "02 Mini instrument cluster battery drain" and this forum post (with pictures!) explains that a poor solder connection causing a short in the instrument cluster is causing excess current problems.

Update 3: I unplugged my Tachometer as the link (in Update 2) above suggests, and my current draw was still in the neighborhood of 0.19 amps. I inspected the board (you will need a jewelers loop or a nice camera) and found no shorts on the circuit board. So now I'm thinking the problem is in my main instrument cluster.

Update 4: I found an aftermarket headphone jack run through an aftermarket Dephi satalite radio unit after removing the head unit and poking around. This might be an a-ha moment - but the current thought the radio fuse looks normal, so not 100% convinced this is the issue. I've removed it. I'll see if my battery continues to die over a few days.

10.51190.51370.51
20.5120-2.54 fluctuates38
30.51210.42390.51
40.43220.51400.51
50.51230.51410.51
60.51240.46
70.51250.51
80.51260.51
90.51270.41
100.51280.51
110.51290.51
120.51300.51
130.51310.51
140.51320.51
150.49330.51
160.51340.51
170.51350.51
180.51360.51
when I pull F4, F21 and F24 all at once=
0.04
when I pull F4 and F24=
0.38
when I pull F4 and F21=
0.1
when I pull F21 and F24=
0.36

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