Electrical woes

[wsmeyer]

2008 X5 4.8 died on my wife yesterday morning. It started, drove just fine with no warning lights and then suddenly 4x4 and other warning lights and as she was pulling into a parking spot it completely died.

At this point the battery was almost completely dead, can't remember but 11 point something volts and the car would reset when the start button was pushed. While removing the battery I noticed the negative terminal was corroded and slightly loose.

I charged the battery up with an AGM compatible charger and it was at 12.7V. Cleaned the terminal and reinstalled. Car drove just fine, no warning lights. Two trips yesterday afternoon roughly 15 miles total with no problems.

This morning the wife takes it and it dies again less then a mile from the house.

I'm going to charge the battery again and take it to Autozone and have it tested as it's only about one year old but really having a hard time wrapping my head around the fact that a battery has enough power to start a car and then die less then a mile later. These have warning lights if the alternator isn't working right?

Any ideas welcome!

William.

[heatmizr]

Intermittent / loose connection somewhere other than at the terminal?

[jfoj]

Get the battery charged, tested and replaced if needed.

Also keep in mind these cars do not really have a Voltage regulator per say.

The battery needs to be registered and programmed as the DME controls the charging Voltage and a good battery and proper programming is key.

Not a problem if the same Amp Hour battery used.

Do you have an AGM battery in the vehicle?? Not sure I would use one of these in one of these vehicles.

Also have you checked the charging Voltage??

I think you can bring up the Hidden OBC menu and display the charging Voltage on the dash?? Search here or on the M5 forum for Hidden OBC Menu.

Proper charging Voltage should be around 13.5 Volts.

A poor mans load tester to to turn the headlights on with the vehicle off, leave the lights on for 2 minutes and the battery Voltage should not drop below 12.2 Volts on a half way decent battery.

And yes, when the battery or charging system goes haywire in these cars, your dash turns into a Christmas Tree!

[wsmeyer]

Thanks for the input guys.

The original battery was AGM so that's what I replaced it with.

Good idea on the charging voltage. I've also got a power supply I'm going to set to 12.7V and hook it up in place of the battery and watch the current draw, obviously with engine off. Does anyone know what it should be? I'm mostly doing it to make sure it drops pretty low when the car is supposed to completely go to sleep, 15 minutes maybe?

[jfoj]

Originally Posted by wsmeyer

Thanks for the input guys.

The original battery was AGM so that's what I replaced it with.

Good idea on the charging voltage. I've also got a power supply I'm going to set to 12.7V and hook it up in place of the battery and watch the current draw, obviously with engine off. Does anyone know what it should be? I'm mostly doing it to make sure it drops pretty low when the car is supposed to completely go to sleep, 15 minutes maybe?

Do not do this.

Leave well enough alone.

The modules typically shut down at about the 20 minute mark as I recall.

You have a bad battery, loose connection and/or a charging problem.

Since there is corrosion on the terminal, this tells me the battery is over charging and/or has a leak.

Just because the battery is only 1 year old does not mean it is still good. A 1 month old battery can be bad.

[wsmeyer]

If the alternator isn't charging the car wouldn't there be a warning light?

The corroded loose terminal is the only reason I gave it another chance but those are all clean and tight now.

[jfoj]

Alternator will not always give a warning, it should but not always.

Also sometimes the Alternator is working somewhat, slipping belt, bad diode, loose connection and this may not trigger a warning.

But also a bad/low battery causes all sorts of problems when the car is started the cranking Voltage drops too low and then the many modules in the car do not communicate properly.

I had a battery with a bad cell in my E46 and the dash lit up like a Christmas Tree. ABS, Traction Control, Brake light and some others.

I was surprised how much a bad battery impacted the car as a system.

Rule the battery out then go from there. You could have something draining the batter as well, this can EASILY be checked with a Voltmeter after an overnight rest.

I have a GMC that has a bad Onstar unit that will drain the battery if the truck sits for more than a few days. I pulled the fuse, but plan on just installing a relay to control the circuit.

[wsmeyer]

So I charged up the battery and got the car back home. Checked with the car running the V across the battery is only 11.99 volts regardless of rpm so it seems like the alternator.

Something else strange though. I've got this battery:

Duralast Platinum/Battery H8-AGM at AutoZone.com - 6 reviews

And am using this charger:

Amazon.com: NOCO Genius G26000 12V/24V 26A Pro Series UltraSafe Smart Battery Charger: Automotive

The charger said 100% but I took the battery to Autozone and their tester said it was good but needed charging as it was only at 63%. They are charging it now and they'll test it again when it is supposedly done in an 1 1/2 hours. Now just deciding whether to wait or just start removing the alternator. They have a Valeo for $242.

[jfoj]

A few things, do not toss in the towel on the alternator yet. 11.99 Volts at the battery means the battery is not fully charged and/or has a problem. Granted this is with the engine running and a semi healthy draw on the battery, but still 11.99 Volts is a dead battery at no load. Not sure what the no load Voltage was, but my guess not what a fully charged battery would be.

A fully charged battery should have a Voltage of 12.6 Volts at the terminal. If more than 12.6 Volts is measured, there is a surface charge on the battery that needs to be removed, usually 1-2 minutes with the headlights on, then wait 5 minutes and see where the battery Voltage stabilizes. If the battery continues to read more than 12.6 Volts, there is a problem, likely an internal short, somewhere in the battery causing the cell Voltage to read too high assuming the Voltmeter is reasonably accurate.

These cars are crazy the way they work and if the battery is low they may not charge properly, especially if the battery is sulfated or has a weak cell.

I am not a fan of the "smart" chargers as much as I am of the old school analog chargers. Matter of fact I am rewiring my first battery charger I purchased almost 40 years ago, long before I could drive, need replace the battery side cable as the insulation is old and cracked. What happens with the smart chargers they often drop back when the Voltage gets higher on the battery. If the battery has a problem it can cause the charger to no fully charge the battery. But if the battery has a problem, it needs to be changed anyway.

The battery testers the parts stores use are typically Resistive/Inductive testers. They do a good job for the most part, however, if the user does not enter the correct battery size, they can and will sometimes condemn a good battery or pass a bad battery.

I have a number of the Resistive/Inductive testers along with the good old 500 Amp carbon pile load tester. Often I use a combination of the 2 before I am 100% happy.

[wsmeyer]

Interesting, thanks for taking the time to type all that. Straight off the charger it read 12.7 but I did not test it again after I took it out of the car. I was surprised at the 11.99 but it does somewhat coincide with their reading of 63%. I was going to pull the alternator and have them test that when I picked up the battery but I decided just to wait and see what happens with the battery first. I'm thinking there's a chance it simply won't charge up much more and they'll deem it bad and give me a replacement.

Of course none of this really explains why it died in the first place.