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X5 E70 (2007 - 2013)
E70 BMW X5 produced between 2007 and 2013. Discuss the E70 X5 with other BMW owners here.

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  #1  
Old 08-12-2014, 12:53 AM
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Question Alternator and battery charging

Looking for clarification of how the alternator performs its charging function and how I might identify a failing/ageing battery or charging problem.

If I understand correctly, the IBS and DME regulate the charging based on battery temp and age; hence the need for registering and/or coding a new battery to ensure it's properly charged. I'm assuming that with all of this engineering that, in the interest of saving fuel and avoiding frying a new battery, the alternator would not charge constantly but would switch on as needed to maintain a proper charge.

I observe on my X5 that there is always a charge of 13.7/13.8 being applied while driving and 14.0/14.1 while idling.

What can I understand from these numbers? Normal operation, aged battery, or something else?
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  #2  
Old 08-12-2014, 01:12 AM
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what is the voltage overnight (in the morning) before starting the motor? (auto-headlights, fan etc off) How old/new is this battery? Do you see it go to 14.4 to 14.7 at all? is this meter accurate or have you tried a second voltmeter?
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Old 08-12-2014, 01:40 AM
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Quote:
Originally Posted by xx View Post
what is the voltage overnight (in the morning) before starting the motor? (auto-headlights, fan etc off) How old/new is this battery? Do you see it go to 14.4 to 14.7 at all? is this meter accurate or have you tried a second voltmeter?
Voltage in the morning, according to the reading in the hidden menu, varies based on how far I've driven but is usually between 12.3 and 12.5. This is also consistent with the digital readout from my battery charger. Have not tried my VOM yet. I have never seen it go above 14.1 and that's just part of a fluctuation that trends more to 14.0. Battery is a little over 6 years old and I got my first "high battery discharge" warning on Sunday when it was stationary and my vehicle was acting up as part of its wake-up/access cycle. Long story on that and part of my DSC thread that I need to update. I still need to pull the new codes since then but, up to now, I get the highest number of codes from the FRM and DIS is pointing to a possible short. I know I'm in the window for battery replacement but since I've had some electrical gremlins I just want to be as sure as possible that it is the battery before spending the $400+ and then still needing to replace something else.
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Old 08-12-2014, 10:38 AM
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oh man... this is a difficult one.
If it's 6 years old, yeah the first reaction is to go swap/code in a new one (would not be a bad idea).
However that 12.3 to 12.5 before starting says it's good (probably has around 70 to 80% charge/capacity left). If it's below 12 then the battery is definitely not good/safe anymore and may leave you stranded (worse in winter/cold time). The normal way is to do a battery load test to check if the battery is still good. There are some DIY method with a min-max voltmeter on youtube.
The 13.7 to 14.1V during drive/idle is ok/good too. Ideally we want to see it near 14.4 but 13.8 is actually good/acceptable too as it's still charging the battery (12.8 is holding, and anything 13.8+ is charging/recharging).
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Old 08-12-2014, 11:32 PM
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Quote:
Originally Posted by xx View Post
oh man... this is a difficult one.
If it's 6 years old, yeah the first reaction is to go swap/code in a new one (would not be a bad idea).
However that 12.3 to 12.5 before starting says it's good (probably has around 70 to 80% charge/capacity left). If it's below 12 then the battery is definitely not good/safe anymore and may leave you stranded (worse in winter/cold time). The normal way is to do a battery load test to check if the battery is still good. There are some DIY method with a min-max voltmeter on youtube.
The 13.7 to 14.1V during drive/idle is ok/good too. Ideally we want to see it near 14.4 but 13.8 is actually good/acceptable too as it's still charging the battery (12.8 is holding, and anything 13.8+ is charging/recharging).
Yes, it's challenging and I'm drinking from a firehouse trying to catch up to all this. I really appreciate your feedback and firm numbers as this gives me a good baseline for understanding as I try to separate the battery from the other suspects. I'll take a look at YT and try to conduct a load test. The problem I'm dealing with is access/wake-up related. Random, appears to be unrelated to battery charge, and impossible to consistently reproduce but the highest number of times it occurs is when the rear hatch is open or being opened. I'm wondering if I'm dealing with a bad connection in one of the lift struts.
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Old 08-14-2014, 03:22 AM
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This morning it was 12.1 before start and 11.5 immediately after. My drive to work is around 7 miles and I always wait the 30 seconds for the alternator to kick in before driving off so the battery is charging the entire time the vehicle is moving. Charging voltage was pretty consistently 13.7 driving in. I checked it 5 hours after arriving at work and it was 12.3, borderline 12.4. Researched the DIY load test yesterday and will perform it when I get a chance.
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Old 08-14-2014, 11:39 PM
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Just ran the min/max test with my digital multimeter. The most interesting part was that it was showing an idle voltage of around 14.4 instead of the 14.1 indicated in the hidden menu. Seems like a rather large discrepancy. So, that's closer to the desired voltage, correct? I also measured a minimum of 9.66 which is very close to being bad, as I understand it.

I welcome your opinions on this but, based on the battery age, low minimum voltage, and winter approaching soon, I'm probably going to go ahead and spring for a new battery and hope that it kills the electrical gremlins. At least I can save a little money on registering it due to having a cable and software and the great knowledge from the stickies at the top.
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