[JackDesmarais]

Hello everyone I have a 2014 BMW 335XI (F30 , N55 ) For the past month if my car is off for over an hour it is bone dead, no lights, can't unlock etc. I've had the car on a charger overnight multiple times and it will start up in the morning, but once again if it sits at all, its bone dead once again. I've had my battery and alternator both checked and both of them check out to be in good condition, My negative and positive terminals are both secured on their posts and I make sure I leave nothing on that could be draining any power. Any ideas for what the issue could be would be greatly appreciated!

Thanks:

[cfm56d7b]

Something is clearly draining the battery if the battery passed the tests.

Were you able to retrieve any stored codes?

[Billfitz]

The dashboard is a known power drain. Do a search.

[Wires]

Either a drain or the battery is bad. Its possible to have a loose plate that shorts it out under vibration.

If the battery is original from 2014, it's most likely the culprit.

[Arkin]

Originally Posted by Wires

Either a drain or the battery is bad. Its possible to have a loose plate that shorts it out under vibration.

If the battery is original from 2014, it's most likely the culprit.

+1 for Wires

The normal battery life is usually about 4 years. OEM BMW may be longer. I have a friend whose battery from 2013 hardly used car just changed this year.

[Billfitz]

I'd be very wary of replacing the battery. That's probably the single most often misdiagnosis here, leading to spending major coin that doesn't fix the problem. A simple test is to fully charge the battery, then remove the negative terminal overnight. If it's dead the next morning the battery is toast. If it holds the charge overnight the problem is parasitic power drain. Obviously you want to do this when you've got time the next day to give the battery one last charge to start the car before you drive to Autozone or the like for a new one.

[im_an_alien]

If your battery goes flat after an hour you have major parasitic drain, you might want to troubleshoot that before replacing battery. My original battery is stamped 10/15 and still strong.

[gameson]

Originally Posted by Billfitz

I'd be very wary of replacing the battery. That's probably the single most often misdiagnosis here, leading to spending major coin that doesn't fix the problem. A simple test is to fully charge the battery, then remove the negative terminal overnight. If it's dead the next morning the battery is toast. If it holds the charge overnight the problem is parasitic power drain. Obviously you want to do this when you've got time the next day to give the battery one last charge to start the car before you drive to Autozone or the like for a new one.

Yes. You should try this first before replacing the battery. An old battery can't hold charge sometime so you have to rule that out first.

[GoranBonn]

If your battery drains in an hour, you have A MAJOR FIRE HAZARD SOMEWHERE! The battery in the car has a capacity of 90 Ah (or 95?), which means if it drains in an hour, your battery is running 90 amps of current through SOMETHING for an hour. At 12 volts, that means around 1000 Watts being spent somewhere. Something must be getting heated up pretty hot with that power.

Disconnect everything, don't drive the car, get it inspected.

[bimmer456]

Sometimes the battery tests good just but then you run the headlights for a few seconds and it tests bad.

[AlmondJayRoM3]

I’m going to assume when they did the battery test they tested voltage and CCA. The tester prints out the status and available CCA and the mechanic will give you the printout.

Assuming that checks out, looking for a parasitic drain is a as simple as connecting a multimeter in series, in ammeter mode after the car has had a chance to fully turn off. Then start pulling fuses. Not going to explain the technique here as if it’s done wrong you can mess up the car, the multimeter or personal injury. Look it up or get it to a mechanic to hunt down the parasitic drain.

You can also use a FLIR to look for hot fuses but most people don’t have thermal cameras

[bdawggg]

Originally Posted by JackDesmarais

Hello everyone I have a 2014 BMW 335XI (F30 , N55 ) For the past month if my car is off for over an hour it is bone dead, no lights, can't unlock etc. I've had the car on a charger overnight multiple times and it will start up in the morning, but once again if it sits at all, its bone dead once again. I've had my battery and alternator both checked and both of them check out to be in good condition, My negative and positive terminals are both secured on their posts and I make sure I leave nothing on that could be draining any power. Any ideas for what the issue could be would be greatly appreciated!

Thanks:

Did you ever figure this problem out?

[Billfitz]

The OP hasn't made any posts since the first one in this thread.

[Tommo3]

Originally Posted by Arkin

+1 for Wires

The normal battery life is usually about 4 years. OEM BMW may be longer. I have a friend whose battery from 2013 hardly used car just changed this year.

Bit short for a life of a battery, I expect 7 years and mine is 5 now.
OEM battery is not made by BMW so is any battery that they were buying at the time. My 18 month old BMW R1250RS had a battery failure as they were using cheap Brazilian batteries at the time (but OEM). The replacement aftermarket is going strong.

[ggrcrash]

Question, what is the approximate mileage on your car? Quite possibly it could be the water pump. It is an electric one and could be on its way out, as in constantly running, aka draining the battery. It happened to me, so you might want to check it out.

[Orion4]

Time to "kill" this thread since OP is AWOL

[E36M3]

If the OP checks this tread again I would recommend a diode test of the alternator.