Battery drain and LED interior/boot lights

[Dan1502]

If you read my response to the thread about BMW emergency services experiences you'll see that I have had a problem with the battery draining and the BMW emergency guy explained that leaving the interior lights on for just a few minutes can cause sufficient voltage drop for the car not to start.

This being the case, I am worried that when getting changes/packing etc in the winter months after mountain biking, I could be left stranded. Do the LED lights use a lot less power and would they help a lot with this issue? I am also concerned regarding changing the lights and the BWM warranty/insurance especially if there is a future electrical issue and (worst case) fire.

[CondorX5]

Battery drain can be for many reasons, but as a start I would have the battery professionally tested under load - it may be that it is the original battery in your car which will be near the end of its life now, or beyond its dates!!! If it is absolutely 100%, I would also look at things like the FSR possibly being faulty - it is a known weakness. Its the final stage resistor of the aircon - becomes open circuit and the fans just whirr on after you switch off, draining the battery quickly.

I don't believe for a moment that a few minutes of interior lights would kill a completely normal battery, nor would the radio - but they would tip an ailing battery over the edge. A battery in tip-top condition can even cope with the headlights being left on for about 10-15 minutes. This winter has been a killer for batteries and many which were just scraping by have died. I often have the boot open (interior lights on) and/or radio while I'm busy in the car, and have never had a battery collapse on me.

I'd definitely check the battery professionally first - have it tested under full load at a battery specialist.

[Dan1502]

Ok, thanks. I did have the lights on for a lot longer than usual so it might just be that. However I would like to be sure I haven't been sold a car with a duff battery. It was showing at the high eighties percent IIRC on the approved car checklist but they haven't left me with a copy of that so I can't be sure. I have discovered a leak in the rear quarter passenger side (not sure where it's getting in) so have to discuss this with them tomorrow. Where's the best place to have the battery tested? Should I trust them to do it?

Oh and how do I check if beyond it's date? It's a 2004 car so if the original would this be the case and should I be supplied with a new one?

[Jalf]

When I gave my X a waxing the other week, with the boot and doors open at various times during the job it wouldn't start after, I have LED puddle and boot lights, bit worrying...

[X5Sport]

The battery should have a week/year code which often looks like WW/YY but may be different. If it's still the original BMW battery then it may be approaching end of life. There is no definite point at which this occurs, but the average is around 6 years. Some are shorter, others longer and all dependant upon how the car is used.

I replaced my Dec04 battery at Christmas. It had been showing signs of problems in the really cold weather and was not holding it's charge. I got a Bosch Sliver Plus as a replacement. Comes with a 5yr warranty.

I would not expect the interior lights to knock out a good battery even if left on for a couple of hours. Are you saying the report on the vehicle battery said 80%? If so that means it's lost more than 1 cell of capacity across 6 cells. What did they mean by the 80% I wonder? It was 80% charged, or it could only retain an 80% charge?

[X5Sport]

[quote=""Jalf""]When I gave my X a waxing the other week, with the boot and doors open at various times during the job it wouldn't start after, I have LED puddle and boot lights, bit worrying...[/quote]

What power are the LEDs? Given that they probably aren't native 12v then they need resistors to drop the voltage. I have often wondered why these LED systems need heatsinks as that tends to indicate a pretty high power dissipation. Has anyone got the resistor values and max power dissipation showing on theirs? From there we can work out the current draw.

Power (W) = Voltage squared / Resistance (Ohms).

Current draw (Amps) is Voltage / Resistance, or also Power / Resistance.

Current draw will be in Amps per Hour. My car battery is 110AH meaning it should deliver 110A @ 12v for 1 hour and then be dead. That equates to 1.32kW

[Dan1502]

The BMW maintenence guy tested it and said no cells were down. The test on the sheet when I collected the car may have been 88% but could have been 92% - I forget and was surprised this checklist wasn't handed over. Perhaps I should ask for it. I know where the battery is but would only want to go and check it for a date if this is potentially a valid reason that it should have been replaced by the dealer prior to sale. I'm not sure how to get to it either. I've used the 5 year Bosch before - very good batteries. The heat output of LEDs worries me too. I don't fully understand the technology but do know from owning various biking and diving lights that heat is an issue and good heat sinks are very important hence my worry about buying cheap ebay angel eyes and also interior lights. The last thing I want to do is cause damage, void warranties or worse.

[X5Sport]

To get at the battery you remove the spare wheel, undo the two 13mm bolts and two 13mm nuts on the air suspension framework (tips of the triangle) lift it out of the way and you're looking at the beastie.

Semiconductor electronic components don't like running much above 70C as you can get an effect called 'Thermal Runaway'. Which is simply that a hot device allows more current to flow, more current means more heat and so on until the device fails in a puff of evil smelling smoke..

Although LEDs last longer and should use less power, they need resistors to reduce the 12v down to what the LED needs. The lost energy in the resistor is given out as heat which has to dissipate somewhere, hence the heatsink. The LED will also need to lose its heat too, but the resistor is where I expect most heat will come from. So in reality, just how much better than bulbs (except in light output) are these LEDs?

[Dan1502]

Makes sense, thanks.

[Dan1502]

Battery date is November 2008 so not that old - about half way through life. Hopefully it should be ok.

But, I had the boot lights on but rest off for the time it took to check the battery date then started it and ran it for a few minutes then accidentally left the door open for 10 mins and it refused to start but then just about started again. Given that I drove it for about an hour last night I'm left with doubts. I've plugged the CTEK in and will see but as I need to discuss another issue with the supplying dealer I'm wondering whether to bring this up.

[X5Sport]

Be intersting to know what the terminal voltages are on the battery. It they're OK then there is another option. There have been a number of issues with the starter motor devloping an internal fault which means it draws more current that the battery can provide so the battery volts drop sharply and as a result either fails to start, or turns over too slowly and struggles to start. This often causes all the on board computers to reset

My starter was changed at just under 3 years. No fault ever showed up on the computer logs, or on the BMW diagnostic system. The fault was found by a tech using a current clamp and intuition working from first principles. It was more of a problem on cold days.

[Dan1502]

Can I use a standard multimeter to check the voltage using the terminals under the bonnet? It's on charge at the moment but I could test it afterwards and in other circumstances if needs be. I think for now I will mention it and say I'm not sure the extent of the problem/what the problem is. Also, although the battery is only just over two years old, the car's only done 4,000 miles in the last 2 years so it could have issues.

[X5Sport]

Yup, no problem. That's where I always check ours from. I think I've probably only done the same sort of mileage as you. I was not allowed to drive for 12 months after a serious back injury and as soon as I got back on the road the gearbox ate itself. Lack of use might be a problem if the battery has been allowed to go dead. Modern starter batteries don't like that and it shortens their life. Mine had gone dead a couple of times but with a charger I kept it going for a wee while before admitting defeat this winter. The battery should show 14.4V on charge when fully charged and around 12.6 - 12.8 off charge in the same condition and depending upon meter accuracy.

[Dan1502]

Ok, I'll check it and see. It's about to be booked in with the local dealer to sort out other issues so I'll get them to check it too.

[pvr]

Not sure if I understand the door open / boot open scenario. When I wax the car, doors and boot etc are open but after about 15 minutes, the lights all go off by themselves.

The only way they stay on is if you open / close in the meantime, as the 15 minutes is reset then. That is why I just leave the lot open for the afternoon that I am working on it.