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  #1  
Old 12-04-2017, 12:43 AM
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Question Quick question about BATTERY VOLTAGE !!

Does anyone know what the battery voltage should read once the e53 has been woken up?

For instance, let's say you have a fully charged battery and leave the car standing for 48 hours.

Then you unlock the car, open the rear door (turning off the interior lights immediately) and measure the voltage with a multimeter directly on the battery terminals (the spare and boot floor are already removed and the back seats are down for access)

If the battery is a brand new AGM (which mine is) and reads 12.77v-12.75v fully charged, is it normal to get an initial reading after waking the car up much lower than that - 12.60v?

Next you pop the rear door latch with a screwdriver (but leave it open) and wait 20 minutes then read the voltage again and get a reading of 12.67v. Another reading taken an hour later shows 12.72v.

My question is: Is it normal for the car to pull so much current from the battery when you unlock it? Has anyone measured voltage immediatly after waking the car up?

Thanks for the help guys hope this made sense!
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Old 12-04-2017, 01:00 AM
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That all looks normal to me. That's not a very big voltage drop at all. Consider that the top voltage is surface charge so the first few 10ths might drop quicker. The recovery after is good too.
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Old 12-04-2017, 01:35 AM
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Sounds normal. Here is a chart showing a battery's charge state.
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Old 12-04-2017, 01:51 AM
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The car does pull a fair amount of current when woken up and those numbers are very normal


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Old 12-04-2017, 11:15 AM
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Here's more info as to the electrical draw when the car is AWAKE. There are multiple system running as soon as the car comes out of SLEEP mode:



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Old 09-16-2020, 03:10 PM
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Car is 2006 X5 3.0i with 136K. Original Valeo alternator.
For the last 6 yrs...doing Test #9...

- Engine idle at 700Rpm, voltage = 13.9V
- Engine off in AM, voltage = 12.2V, even with brand-new battery.

I have heard that a battery at rest, as long as > 12.1V, it is OK?
Of all the cars I have owned in 25 yrs, I never get anything more than 12.4V, even with new battery...

Any ideas?
Is this voltage of 12.2-12 4V normal?
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Old 09-17-2020, 08:38 AM
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Quick question about BATTERY VOLTAGE !!

For a 12v battery to show 12.2 to 12.4
Is very normal. Old or new. The resting voltage is based on the chemical reaction that develops just over 2.0v per 6 cells.

The 13.6ish really should not be called battery voltage though we all.say that it's the alternator output voltage happens to be connected to the battery terminal. The 13.6-8 number must have been decided as a good value to supply a decent amount of charge to the battery without over charging it.

Some newer cars will disconnect the battery from the charging circuit so they cant over charge.
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