XSeries-forum

Whilst I was repairing my wobbly door handle I had the boot and a couple of doors open for a couple of hours, plus I did sit there and mess about with radio stations as well, all of this drained the battery to a point that the car wouldn't turn over.
Chucked it on the trickle charger overnight and all was well this morning, checked voltage across the terminals under the bonnet and a healthy 12v.
Locked the car and thought all was good, then about 7 hours later the alarm went off, checked the voltage again and it had dropped to 11.72v, is that enough of a drain to trigger the alarm?
Thought I'd try and see if the car was drawing any current whilst in "sleep mode ", I'll try and post some pics of the readings, but in case I can't I'll try and explain.
Meter set on amps and switched to 20A on the dial connected it across the under bonnet terminals and it read OL, does this mean it's drawing a lot of current and the meter is out of the settings range or am I reading it wrong.
I then thought I'd see if the battery was getting charged when running, meter reading 13.9v when car just ticking over, I think that's ok.

How old is the battery??....

Not sure to be honest, I might take a look to see if there's a date on it.

Fully charged and with the car asleep you should be seeing at least 12.6V. You will need to leave it for 4-5 hours after last use/charging before you measure it. A brand new, fully charged battery could show as much as 12.8V (AGM Type). I measure under the bonnet so leave the bonnet open enough to avoid the alarm switch and just lock the car.

Anything below 12V with the car asleep indicates at least one dead or dying cell. My X6 battery died without warning a couple of weeks back. It was falling to 11.5V after a couple of days without use. That one was 8 years old.

If it's an AGM type battery then you should be seeing 14.4V with the engine running at a fast idle and everything else switched off. A badly depleted battery will pull that down though.

No date on battery, but I did see that the indicator is saying it needs recharging, I'll add a couple of pics to show.
I still can't get my head around the reading when I measured any current draw.

If the car is awake it could be drawing more than 20A. Mine draws >60A without the engine running. You need the car asleep, and use a current clamp device (measures the magnetic field caused by current flow) to measure a current draw without disturbing the electrics or incinerating your meter

I think my first phone call in the morning is to the battery shop, lol.
I already have a price from BMW of £120, so I'll see what others are offering.

How do you test for a drain under the bonnet.
I have always done it at the battery taking a terminal of and bridging it with the meter.(on amps setting)...

Not sure you can. Voltage yes, but the current draw needs to be at the battery terminals - at least I don’t think it works.

By no means an expert, but I thought the terminals under the bonnet were merely an extension of the battery ones, well at least the positive side, earth is just an earth.
So would that not give you a similar reading if you clamped around the lead under the bonnet.

You might be right. ISTR my E53 having a couple of smaller wires coming off the battery as well as the main feeds. I think they were to supply low power circuits in the event of the airbags deploying as the main feed is cut by a small explosive charge (for safety). Mine had some form of telematics as well as the in car phone and that stayed powered in the event of an accident. That tech will depend upon the year though.

You can't measure current without breaking into the circuit so the the meter is inline unless you have a clamp meter which goes round the battery lead ,if you put it across Id say the fuse should be blown or your meter would be on fire as you are shorting out the battery unless I've picked it up wrong ?

You are right, the correct way of measuring current is to break into the circuit or use a clamp meter, basic schoolboy error on my behalf.
Although it was about 40 years ago since I did my basic electrics course as part of my engineering apprenticeship, ( not as an electrician though ).
Hopefully it's just a new battery that's needed and nothing more sinister

11.7 volts is goosed, you never want to see less that 12.5 on a 12v battery - after a full charge on a smart charger it should read nigh on 13 if it’s brand new and in tip top condition, then if left with no load on the voltage reading will settle out after 12 hours or so - not something you do that often when your battery is in the boot!

Careful where you buy your battery from, some places are easier to return to than others for warranty claims, and if you buy online they’re not that easy to post back.

Funny you say about the interior lights, if you press the roof button they all go out apart from the lights in the boot, so I fitted a switch so I could turn my boot lights off - how anal is that - I must win best prize for most unnecessary mod.

New battery purchased and fitted, reading across terminals before fitting was 12.6v.
Used the car for an hour or so yesterday afternoon and all was fine, stopped and started a couple of times.
Parked up when back home and locked the car via the remote about 4ish, was woken up this morning about 4ish by the alarm going off
I just switched the alarm off and left it at that, went out this morning and measured the voltage at the terminals under the bonnet, 12.3v, should this worry me, and is this enough of a difference to set the alarm off.
Does the alarm look for voltage drop or current usage to set it off.
I've now set the alarm again to see how long it takes before it goes off again.