E39 Battery drain guru's

[rusteee 52]

Hi guys

Got 99 problems and the E39 is about 98 of them haha. Have a battery drain issue on the E39 540, and wondering if there are any common issues that would cause this? Basically, last drove the car Saturday on about a 140km trip then parked up at home, never missed a beat. Came out on Tuesday the following week to get something out of the car and it was completely dead, wouldn't unlock, no lights, and quite possibly has damaged the battery as my meter was measuring 2volt. Put in on charge, it was so low I had to use a dummy load to get the smart charger to work. Charged on a 8amp cycle for 6 hours to see what happened, and the battery voltage rose to 12.4v and started the car no issue. Once started the voltage went to 14.2v so I figure that rules out the alternator unless they can be tempermental? and it was rebuilt just over 2 years ago. No interior or exterior lights were left on, the climate control fan does not run on, the in car phone is off and the boot light is off. Are there any hidden items that may cause this? Any help appreciated

[aja540i 1896]

Have you ever replaced your ignition switch?

[rusteee 52]

No, don't think it has ever been done looking at the history. Do these cause issues? When I left the battery connected again over night, the next day it was down to 11.2v

[aja540i 1896]

I did mine as preventative maintenance, these cars go mental when they start to fail. You could also grab your multi meter and wait 15 minutes after you turn it off so it goes into sleep mode then check the current drain at each fuse to narrow it down.

[rusteee 52]

That's a damn good idea. will have a look into replacing the ignition, is there any tell tale sign that is could potentially be failing? It def goes into sleep mode but something un-obvious must still run if it completely drained the battery in that time. The battery is 2 and half years old so hopefully ruled that out unless its buggered now.

Seen you boosting up Wairau the other day in the mighty 318, could have given you a race in my beast of an L300 hahaha

[hotwire 352]

6 hrs is nowhere near enough time to charge a battery from 2v. It will only be partly charged with a surface voltage sitting on top.

Charge it for at east 24hrs & have it tested.

12.8v is fully charged but only after surface voltage has disappeared.

Fan isn't always heard when the FSR is faulty

They generally take over 20mins to go to sleep

11.2v overnight could be highlighting a problem, but also. the voltage would have dropped after the car sat again & the battery only partially charged.

These, like many cars nowadays are a pain to check current draw - to eliminate anything you have to wait each time for it to go to sleep

Start by charging the battery properly first.

Ign switch - yes they fail BUT wont cause current drain, not that i have ever seen anyway.

Edit. Battery likely to still be ok - flattening a good battery wont kill it. Sometimes old ones refuse to respond.

That said - it could still be faulty

Edited March 10, 2016 by hotwire

[aja540i 1896]

That's a damn good idea. will have a look into replacing the ignition, is there any tell tale sign that is could potentially be failing? It def goes into sleep mode but something un-obvious must still run if it completely drained the battery in that time. The battery is 2 and half years old so hopefully ruled that out unless its buggered now.

Seen you boosting up Wairau the other day in the mighty 318, could have given you a race in my beast of an L300 hahaha

Probably would have won!

I have heard about all sorts of wierd things happening to the electrics when the ignitiion switches go, not necessarily draining the battery but it wasnt that expensive from memory. I would leave the battery on a longer charge first though, it shouldnt be poked at that age unless it has been abused, BMW say 10 years is the life of a battery!

[hotwire 352]

Batteries can fail off the shelf - seen it a few times over the years.

The amount of people I see at work that say it cant be the battery - it's only 2 yrs old. Guess what!

Most BMW OE batteries (Varta) last 10 yrs +, some less. Have replaced a few Varta batteries in 2 - 3 yr old Navara utes, so they aren't all built the same.

[rusteee 52]

Yea, I'm aware 6 hours is no where near enough to charge (sparky), but the car sits outside un garaged in a west Auckland suburb, not prepared to leave it overnight with the boot open and extension lead hanging out in there haha, so connected it back up just to be safe. Its been charging all day today and still charging now as only 3 quarters according to the charger. As you say, I would like to give it a good 24 hours. Might have to do the tedious task of waiting each tim e and current check one by one....

I would have thought if the battery was faulty/dropped a cell it would immediately be noticable or the charger would fault as would mess with the charge cycle. It worked perfectly when the car was last used no sign of it dying as car started with ease. Don't actually know when it went flat, just noticed it on the Tuesday.

Edited March 10, 2016 by rusteee

[hotwire 352]

Charger wont necessarily reveal a crook battery. Also bear in mind that the battery will start the car from anywhere from full charge down to about 1/4 charge ish - a fine line between start/no start. If the car starts - you have no idea of the actual state of charge of the battery at that time, equally if just off the charger - it could still be "flat" but start on the surface charge.

Just like a jump starting a car with a flat battery, leave it running for 10 mins & the car will start on its own battery - on the surface charge the alternator has just poked into it.

The battery is still "flat" though. Leave the car sitting for an hour - the surface charge has dissapated & the car wont start again.

[rusteee 52]

Indeed, thats how those little jump start packs work too by boosting the surface voltage, but usually, like when the old battery started to die you would notice the starter hemorrhage when starting or would struggle, always started though. When I put this one in, there was an instant difference in cranking speed, and hadn't changed even when last started Saturday arvo. So something has happened since turning it off, and leaving it sit, as Prior to Saturdays drive it sat for over a week with no issues. I'm pretty confident that the battery is not the problem, but I might borrow my mates battery discharge tester and check it just to be safe.

[hotwire 352]

A tired battery will make the starter labour due to its inability to supply the current required (even when fully charged) a good battery though will supply the required current down to a lower state of charge level.

Just to complicate - batteries can self discharge too. Not a common scenario & usually on older batteries.

[rusteee 52]

I don't think this is the case, as it would have been noticable unless it died instantly.

Edited March 10, 2016 by rusteee

[TermiPeteNZ 1302]

An E53 X5 i was looking at buying in Lower Hutt has the aircon unit (controller in the dash) removed by the dealer as it was working fine but drawing too much power - it would flatten the battery overnight. Prob the same unit type as your E39 at a guess.

Edited March 10, 2016 by TermiPeteNZ

[rusteee 52]

That will be one of the first things I check, it appears to all be off but you never know. Will do the load testing on it this weekend and see whats up

[allan 295]

Hi Russell my experience with this on the 530 was two problems. First the final stage heater control unit was on its last legs this not only gave weird heater control situations as well as a flat battery over a few days. The second was the battery it's self, gen BMW about 8 yrs old it was after it had been charged fully and then load tested this showed it lost the ability to retain a charge of sufficient umff and after a couple of days was flat again. In my case once the FSU had been replaced I took the risk and tried it with the then unknown weak battery but with in a couple of days back came the flat battery problem. So after the battery was replaced all was good no more starting problems best of luck be interested to know what you come up with.

[rusteee 52]

that was one of my suspects, but the heater controls are all working perfectly fine, will check anyway. I think it is definetly a drain issue as the battery was very dead, usually it will still sit a good 10 or 11v even with a dying battery, but cant hold the crank current. If it comes down to it, I will buy another battery and see how it goes but would rather do some testing first. Cheers for the advise

[rusteee 52]

Does anyone know at what RPM the alternator kicks in, if it does drop off? Battery was fully charged as of yesterday sitting at 12.8v. Started the beast and it went to 14.1v idling cold at about 800 rpm. Took it for about a 20 minute drive, then checked the reading whilst the car was still running at idle, it was sitting at 12.9v, so I turned the lights on and it dropped to 12.5v idling at 450-500 rpm. Might try hook up the bluetooth obd and see if I can get live readings while driving around.

[aja540i 1896]

According to mr Bentleys book, with fans lights rear defroster and wipers going, at 2000 rpm, battery voltage should be above 12.6 if its charging properly.

[rusteee 52]

Sweet, cheers for that, will rip into it and see whats up

[hotwire 352]

Should be way over 12.6v @ 2000rpm. 12.8 is fully charged static, it ought to be charging @ 14v + on these cars. Was a different story years ago with the old Lucas ACR's where they were rated to 13.8v max & they were less efficient at idle.

500 rpm is very low for idle speed - i would expect it up around the 700 mark. Once excited, an alternator will generally stay in at idle & cover lights, not at 500 rpm though.

Try holding about 700 -50 rpm & recheck charging voltage.

[aja540i 1896]

Would expect to see up around 14v at 2000 rpm with no loads switched on, but it will drop with all the load items going, this test is for alternator output under load, taken from the bentley manual.

[hotwire 352]

"MOST" cars alternators will charge at 14v at under 1000 rpm with lights on. i see this every day of the week. More load will obviously drop the voltage though at this rpm though.

450 - 500 rpm is very low though - i certainly would expect voltage to drop with lights on

[westy 614]

Does anyone know at what RPM the alternator kicks in, if it does drop off? Battery was fully charged as of yesterday sitting at 12.8v. Started the beast and it went to 14.1v idling cold at about 800 rpm. Took it for about a 20 minute drive, then checked the reading whilst the car was still running at idle, it was sitting at 12.9v, so I turned the lights on and it dropped to 12.5v idling at 450-500 rpm. Might try hook up the bluetooth obd and see if I can get live readings while driving around.

You can watch some live data, including charging/operating voltage on the cluster. Just google hidden display.

Also has engine temp, fuel level each side etc

[hotwire 352]

The reason batteries last significantly longer in BMW's compared to Navaras, and Prado and most other cars is the battery location.

Quite simply BMW are smart in putting the battery in the boot , it is a cool part of the car , t

Those who put them in the front with the engine subject the battery to extreme temperature cycles every time the engine is operated at full temp

In back up power systems we calculate battery life based on ambient temperature.

For 20c 17 years is normal

At 30c this comes down to 11-13 years

Move to 40c and you are looking at 3 to 4 years

At 60c expect 18 months

Its not rocket science why modern cars kill batteries, higher powered engines generate more heat in a smaller space and cook the crap out of them except those lovely thoughtful designers at BMW .

For your battery problem sort the basics out first and then you will know what you need to find.

Is the battery fully charged, does it perform under a load test, does it hold a charge

If the answer to all of the above is yes then, it is the car sucking the battery flat. At that point you can then start looking at what the current draw is and try to work out which device is sucking it.

Yes meant to substantiate the temp/boot thing, & yes 20deg celcius is the ideal operating temp for a battery.

That said there is more to it with the Navara thing - batteries don't get overly hot in them - certainly not to the 60 deg 18 month level. I suspect it is a "different" Varta as far as quality.

The modern batteries composition is designed to more handle higher under bonnet temperatures & for the most part they do, batteries are still usually getting to the 6 yr old mark before dying/cooking.