DIY how to test a BMW E39 battery & alternator (discussion)

Today, someone posted that their BMW battery didn't have the date stamped into the terminal lead:
- E39 (1997 - 2003) > Stranded won't start

Originally Posted by bwaysteve:
There are no dates on my terminals.I bought the car in 2001...so I replaced with a BMW battery.

My question, to the tribe, is whether it's only the original (factory) BMW batteries that are date stamped in the terminal lead - or - if all BMW-branded batteries are supposed to be date stamped in the terminal?

I always carry a Voltmeter ($3-4 from Harbor Freight) in my cars in case I need to check the battery etc.

Recently, a new product comes out: "cigarette voltage checker".
You can get it online for about $6-8/each.

I have this "cigarette voltage checker" in the glove box just for a quick check (this way you don't have to open the hood or trunk to check the battery).
Kind of a "lazy" way to check the battery from the cockpit LOL.

Here is another link to:

Equus 3721 Battery and Charging System Monitor:
http://www.amazon.com/Equus-3721-Bat.../dp/B000EVWDU0

Originally Posted by cn90

Here is another link to: Equus 3721 Battery and Charging System Monitor:

Since Amazon links may die over time, I've taken the liberty of including Cam's helpful hint in a screenshot below.



In addition, I just referred (for the umpteenth time) someone to this thread and realized that my engine-mounted battery charging picture wasn't clear as to where the positive & minus connection points were.

So, I circled them to make them more clear to a newbie.

For the crosslinked record, cn90 proposed a novel way to boost a dead battery when, for whatever reason, neither the trunk nor the hood can be accessed:
- E39 (1997 - 2003) > battery dead- doors open trunk locked- really mad! help

Originally Posted by cn90

If one is desperate (assuming one had already used QSilver7's instructions and it didn't work), then use this trick below. I bet you money the dealer does not know this trick!

This is a little known secret, on the driver's side chassis, if you crawl from underneath looking upward, there is a positive post that feeds the starter motor.

1. Stand outside looking at the LEFT FRONT tire, look at the rear part of the tire, follow this inward about 12" or so, you will see the positive post feeding the starter motor.
Lying on your back and reaching your hand in, you will see this positive post (a large makeup $5 mirror will be very useful).

Using appropriate alligator clips & wire:
- One clip goes to this positive post.
- Another clip goes to transmission housing or any ground
(Just make sure you don't short the wires).
- Then connect both wires to a donor car's battery (any car with a good 12V battery).

Now you can use your key remote to open the door, voile!

2. Now if you cannot reach the positive post due to low ground clearance:
- Jack the front driver's side up and
- Place a jackstand under the subframe. This is very important if you don't want to be crushed!
- Then do the jumping of (+) and (-) terminals as mentioned previously.

For the cross-linked record, today, there was a good discussion of battery tests here:
- E39 (1997 - 2003) > Battery Voltage

Great thread, subscribed.

Darn it, I forgot to get the vent tube when I picked up my battery this morning. Thanks to the excellent links in this thread, I know that I can't "reuse" the one from the OE battery since its a different location.

Plus, let the car go to sleep.

BTW, kudos as well for the very clear unlocking directions. Previous posts on different forums were confusing and I never tried. After my new battery is in, I'll unlock and check readings.

Unlocked my cluster this AM. After a night sitting, the car shows 13.6V with the engine running, 11.9 without. Good to go?

Interstate H9 had a prominent "Made in Germany" sticker on it. I know Johnson bought Varta in 2002 -- maybe they still have some factories over there? The connector lined right up with the vent tube, I didn't need the extra length. Of course this is M5 specific, not E39 but FYI.

Also, I found via the date stamp on the old Exide battery that it was only 2.5 years old. I know these cars are hard on batteries and PO didn't drive it much. But better doublecheck the warranty I get on the Interstate.

11.9V is considered fully discharged IIRC.

11.9V is considered fully discharged IIRC.

!!?? That would suck. The battery is brand new. If it was fully discharged, would it start the car? She's firing right up.

Charging my battery in-situ (apparently) blew up my instrument cluster:
- Warning: I charged my battery today & apparently killed my instrument cluster & MID

Coming here for help, I quickly realized this thread is harder to use than it should be because information is scattered about.

To consolidate what's above ...

WARNINGS:

• ALWAYS charge a BMW E39 battery OUT of the vehicle!
• NEVER disconnect a battery while the engine is running!
• Try to wait at least 16 minutes (with the trunk open) before removing the battery (just wait for the trunk light to go out)
  
  • Always charge the battery before running the tests below (otherwise, a battery that is simply discharged may test worse than it actually is)
    
  • Remove surface charge before running open-circuit tests below (otherwise, a battery may appear healthier than it really is)
• ALWAYS install the vent tube properly!

Suggested method of removing the battery: (see pictorial thread here)

1. Remove key, unlock all four doors, and exit the vehicle
2. Open the trunk (note the the trunk light will come on and stay on)
3. Some say wait at least sixteen minutes (or at least until the trunk light goes out)
   • For details, see: How to disconnect the battery to prevent the 16-minute BMW transport mode from disabling the remote key and other items (1)
4. Without opening any doors, disconnect the battery terminals
   • First disconnect the negative terminal (10mm socket wrench)
   • Then disconnect the positive terminal (10mm socket wrench)
5. Remove the E39 battery hold-down metal cross brace (13mm socket wrench)
6. Note: Some say, if you need to 'reset' electrical components such as a DICE Silverline, once the battery is removed from the vehicle, to short the positive and negative terminals with a wrench for five minutes to "allow excess stored charge to bleed off".

How to measure voltage:

• Most people use a digital multimeter (although an analog multimeter 'should' work as well - the Bentleys specifically say to use a digital multimeter).
• IMHO, the Bentleys are confusing in describing when to load and when not to load the battery!
  • I "think" the following applies:
    • Battery open-circuit tests: Bleed surface charge as described (e.g., let the battery sit for 2 to 3 hours after charging and before testing)
    • Battery under load tests: Load the battery as described (e.g., turn the high beams on for 15 seconds before testing & leave the load on while testing)
    • Alternator output tests: Load the alternator, as described (e.g., wait 15 seconds, turn on lights, fan, wiper, & rear defroster & leave the load on while testing)
• If you don't have a digital voltmeter, one can unlock the E39 instrument cluster to read battery voltage on your "high cluster" instrument display:
  • Hold down the right button (about 10 seconds) until test 01 shows on the display
  • Press the left button once to show the results of test 1 (i.e., your VIN)
  • Add up the last five VIN digits, e.g., GZ12345 = 1+2+3+4+5=15
  • Press the right button once to go to any LOCK=ON display
    • Note: This is different (simpler) than the instructions which say to go to test #19 (but going to test #19 will also work just as well)
  • Press the left button repeatedly until it displays that number (15 in this example)
  • With that number displayed (e.g., 15), now press the right button once (this should unlock the display)
  • To see battery voltage or alternator output voltage, press the right button repeatedly until you see test #09 on the display
  • Press the left button to view the results (e.g., 13.8 volts at idle or 12.6 volts with the engine off)
    • Note: You can leave the display in this position while testing and/or driving but when you turn the ignition off, you'll have to perform the unlock procedure anew.

How to remove surface charge for open-circuit voltage tests:

• If the car has been driven recently or if the battery has recently been charged, surface charges may cause battery voltage to read higher than it would otherwise
• To remove excess surface charge
  • Allow the battery to sit for 2 to 3 hours before testing
  • Or, turn the high beams on for 5 minutes & then wait 5 minutes more with the ignition off before testing
  • Or, apply a 15 second load of 1/2 the battery's cold-cranking amperage & then wait 5 minutes before testing

How to load the battery for so-called closed-circuit tests:

• Note: Apparently, you test the battery voltage while under this load! (correct me if I'm wrong!)
• Always fully charge the battery first (as a discharged battery may read lower than it would otherwise)
  • Apply a 15 amp load for fifteen seconds before testing (turn the high beams on for 1 minute with the ignition off)
  • Or, apply a 200 amp load for one minute (as stipulated in the Bentleys ... where you get a 200 amp load, I don't know)
• Test the closed-circuit voltage while the battery is still under this load!
  • Note: I'm assuming you test under the load (and not after the load is released); but the Bentleys are confusing to me on this point!

How to load the alternator at engine idle for alternator output tests:

• Note: Alternator output should be tested with the engine idling under the following four loads after at least 15 seconds of idling (for the alternator to ramp up):
  • Turn the high beams on
  • And, turn the rear defroster on
  • And, turn the fan on (full force, I guess)
  • And, turn the wipers on (to the regular setting, I guess)
• These loads should be left on while the alternator output tests are being performed.

AutoZone free test: (see pictures here)

1. Drive (if you can) to Autozone.
   • If you can't drive, you can bring the battery or alternator to them for testing
   • HINT: If you do drive, put jumper cables and/or a spare fully-charged battery in the trunk (just in case)
2. Once at Autozone, ask the parts guy to test your vehicle.
3. They will hook their instrument directly to the battery to run the following three tests:
   • Battery:
     • With the key out of the ignition ...
     • They will apply a light load to bleed off excess charge
     • They will test the open-circuit voltage of the battery
     • They will enter the cold cranking amperage of your battery
     • They will apply an appropriate load (based on the CCA value)
     • They will test the closed-circuit-after-load voltage of the battery
   • Alternator:
     • They will ask you to start your vehicle
     • They will NOT ask you to turn anything else on (at least they didn't ask me today)
     • They will test the alternator using three tests
       • Amperage output
       • Diode integrity
       • Lamp integrity (i.e., ability to light the dashboard warning circuit)
   • Starting System:
     • They will ask you to restart your vehicle
     • Their instrument will make before/after measurements to test your starting circuit

Home DIY: (see pictures here)

1. Visually check the battery and cables for tightness, corrosion, or physical damage
   • Be mindful of the explosive charge on the battery positive cable.
   • See: How the battery disconnect explosive charge works in an accident (1)
2. Note the date stamped into the negative terminal of a BMW battery (or labeled on the outside of an aftermarket battery).
   • Note: My dealer-replaced BMW battery did NOT have a date stamp in either terminal!
3. Note the color of the BMW battery specific gravity indicator in the #2 cell (counting from the negative terminal):
   • Green === adequate charge
   • Black === inadequate charge
   • Yellow === defective
4. The battery needs to be in the 'fully charged state' to properly test the open and closed circuit voltage readings
   • Use a low-current battery charger of 6 amperes or less (never exceed 16.5 volts charging voltage!)
5. Open-circuit voltage quick test:
   • Note: Bleed off excess surface charge as explained above.
   • >= 12.6V@80°F === fully charged (Note: May be up to 13.8V.)
   • >= 12.4V@80°F === 75% charged
   • >= 12.2V@80°F === 50% charged
   • >= 12.0V@80°F === 25% charged
   • <= 11.7V@80°F === fully discharged
   • Note: If the open-circuit fully-charged voltage is less than 12.4 volts, recharge the battery & retest.
6. Closed-circuit voltage quick test:
   • Note: Load the battery for this so-called closed circuit test, as explained above & test the voltage while still under that load!
   • > 9.6V@80°F === OK
   • > 9.5V@60°F ===OK
   • > 9.3V@40°F ===OK
   • > 8.9V@20°F ===OK
   • > 8.5V@0°F ===OK
7. Charging system quick test:
   • With the ignition idling for at least 15 seconds (and with the high beam, rear-window defroster, interior fan, & wipers on), check the voltage in the following FOUR locations (they should all read the same to ground):
     • with the ignition off, across the battery
     • with the ignition off, across the engine-bay (+) and (-) terminals (see pictures posted prior)
     • with the ignition off, on I6 E39s, pull back the rubber cover to check at the alternator #30 B⁺ post (see diagrams posted prior)
     • with the ignition off, disconnect the alternator harness connector, and then, with the ignition on, check at the alternator #15 field pin to ground (see diagrams posted prior)
   • Battery voltage should be >= 12.6V@80°F with the ignition subsequently turned off after a one-minute load and between 13.5v and 14.5v with the engine idling & the following four loads (high beam, rear defroster, interior fan, & wipers)
     • WARNING: Never disconnect the battery while the engine is running!
8. If any tests above fail, you may wish to check wiring & fuses.
   • See: Where to find E39 fuse boxes (1) (2) (WDS) (WDS.ru) & how to find the front passenger seat undercarpet fuse panel (1)
9. Check charge circuit lamp
   • Locate the blue wire coming from terminal 61E of the alternator harness connector (see diagrams prior posted)
   • With a piercing test lead and with the alternator harness connected, pierce that blue wire with your positive test lead
   • Then turn the ignition key to the on position
     • The charge lamp should light on the dashboard
     • And you should see <= 1.5 vdc on your meter
   • Now start the engine
     • The charge lamp should go out on the dashboard
     • And you should see >= 8.0 vdc on your meter
10. Check the electrolyte level & specific gravity:
    • Load the battery with 15 amperes for 1 minute (turn on the headlights with the engine not running)
    • Shut off the ignition & remove the key
    • Open the trunk & allow the car to sit for at least 16 minutes
    • Check the electrolyte level
      • Remove the battery from the vehicle
      • Remove the E39 steel hold-down strap
      • Peel off the two stickers on top of the BMW battery
      • Pry up all six cell caps using a small 1/8th inch screwdriver (be careful as it's very easy to damage the caps!)
      • Electrolyte level should be to the fill line which is 1/4 inch or 5mm above the top of the plates at the very bottom of the internal black plastic depth indicator
        
        • Note: The BMW battery has an L-shaped landing (which clearly shows where the electrolyte level should be)
      • Top off with distilled H₂O, allow time to mix, & recharge, if necessary (since you've, in essence, suddenly diluted the existing electrolyte)
    • Check the specific gravity:
      • Check the electrolyte temperature with a thermometer.
      • Place a hydrometer into each cell & write down the values
        • 1.265@80°F === OK
        • < 1.265@80°F === DISCHARGED
        • Note: Add 0.004 to the hydrometer reading for every 10°F above 80°F & subtract 0.004 for every 10°F below 80°F
        • Note: See this thread: What tool do most of you use to test the specific gravity (hydrometer) of the battery
      • If the average specific gravity for all six cells is below 1.225, remove the battery from the vehicle and recharge & test again.

Ways for a battery to 'die':

• Over time, the electrolyte, which is constantly replenished by electricity from the alternator, is chemically depleted, causing very gradual loss of stored charge.
• The 'paste' on the plates crumbles off, over time, and eventually shorts out the electrical plates, one by one, each diminishing the capacity until you go below the thresholds below.
• Overcharging can heat up the plates, buckling them, and causing the paste on the grids to fall off the grids.
• Each time a battery runs down so far that it won't start the car, it loses a small percentage of its capacity, due to insoluble compounds being formed in the depletion process.
• Disuse causes the chemicals in the paste to form insoluble compounds which slowly decreases the ability of the battery to be chemically & electrically recharged.
• Physical damage causes leakage of electrolyte.
• Oxidation on the terminals causes high resistance to electron flow, causing the battery to 'appear' weaker than it is.
• Cold weather slows down chemical reactions, exacerbating any of the problems listed above (and, if the battery is discharged, the fluid can literally freeze, the ice causing physical damage)
• The vent, if not connected, and if blocked, can cause chemical and physical damage.
• Prolonged overcharging can cause electrolyte to evaporate, causing the fluid level to lower below the plates, which causes insoluble compounds to form on the area of the plates not immersed in electrolyte.

What battery to buy & how to change it properly:

• OEM specs are Group 49, 720 CCA, vented
  • BMW 61.21.8.381.762
  • USA 729905-10
  • EN 12V 90Ah 720A
  • SAE 160 RC 720 CCA.
• The trick to finding good replacements is to look for these SIZES (details here):
  • Group 49/DIN H8
  • Group 95/DIN H9
  • Group 48
  • Group 94R
• Aftermarket batteries known to work in the E39 (1) (2)
  • Duralast 49-DL (Autozone, Walmart) <=== this is the most often recommended battery!
  • Duralast Gold 94R-DLG, 730 CCA, 140 min reserve capacity
    
  • Duralast Gold 95R-DLG, 850 CCA, 110 min reserve capacity
    
  • Duralast Gold H8-DLG, 760 CCA, 100 min reserve capacity
  • Deka 649MF
  • Interstate Mega-Tron II
  • Interstate Mega-Tron Plus
  • Interstate MTP-93
  • Interstate H9-110VW (MTP-H9)
  • Batteries Plus Werker 95R-LI
  • Bosch 94R 730B (Pep Boys)
  • Bosch 49-850B (Pep Boys)
  • PS Platinum 95R850PP (Pep Boys)
  • Optima 34R
  • Odyssey 1700
  • Sears Die Hard 49
  • Super Start 94REXT (Kragen, O'Reilly)
  • Super Start 94REXTJ (Kragen, O'Reilly)
  • Super Start 95R72J (Kragen, O'Reilly)
  • Exide Classic 49-60 (850 CCA)
  • Exide Classic 94R-60 (730 CCA)
  • Exide Global Extreme L4/94R-E108 (790 CCA)
  • Exide Global Extreme L5/49-E108 (900 CCA)
  • Napa Legend International, BAT 7595R, 850 CCA, 190 min reserve
  • Napa Legend International, BAT 7549, 900 CCA, 185 min reserve
  • Napa Legend International, BAT 9849, 850 CCA, 170 min reserve
  • Napa BAT 8449, 900 CCA, 185 min reserve
• Make sure you get a vent tube kit!
  • See also: What battery (1) & what battery options (1) & what battery maintenance (1) & battery electrolyte (1) & battery replacement DIY (1) (2) (3) & how NOT to change the battery (1) (2) (3)
• Note: Some people choose batteries, for some strange reason, by marketing warranty ...
  • If you're one of those, see this: Whether or not a replacement-part lifetime warranty make sense (1)

Note: BMW E39 instrument cluster anomalies are known to be caused by low voltage issues. For details, see:
- One user's experience debugging a half-dead instrument cluster (1) which, after testing the fuses (1) battery & alternator (1) thankfully turned into an alternative battery search (1) and a simple battery replacement DIY (1)

OK Blue, big clarification requested. You say above:

If you don't have a voltmeter, one can unlock the low or high instrument cluster and read closed-circuit battery voltage with the ignition on position #2 with the engine not running and the cluster set to test #09.

So the cluster measures closed circuit with the engine off. You test that this way:

Load the battery with 15 amperes for one minute (by turning the headlights on with the ignition off)

And look for these numbers:

# 9.6V@80°F === OK
# > 9.5V@60°F ===OK
# > 9.3V@40°F ===OK
# > 8.9V@20°F ===OK
# > 8.5V@0°F ===OK

Right? Just did that, and I'm at 11.7, way above 9.5. So is this battery powering like a brand new one should?

Originally Posted by Edgy36-39

big clarification requested.

I must admit I am thoroughly confused when I read and re-read the Bentleys as to WHAT loading/bleeding/running steps need to be done prior to the three specific tests (open circuit voltage, so-called closed-circuit voltage, & alternator output voltage).

I think we need someone (who actually knows the answer) to pitch in.

IMHO, the Bentleys are supremely confusing in describing when & what to bleed/load/run before or during the battery tests!

• I "think" the following applies for bleeding/loading/running:
  • Open-circuit tests:
    • Bleed surface charge
    • Test not under any further load
  • Closed-circuit load tests:
    • Load the battery
    • Test while under this load <=== I now 'think' this is the right way (and I changed the post prior to yours to reflect this)
  • Alternator output tests:
    • With engine running
    • Load the alternator (lights, fan, wiper, defroster)
    • Test while under this load

Assuming that is correct (NOTE: IT MAY NOT BE!) ... then this is the best I can come up with for the bleeding/loading/running steps:

How to remove surface charge for open-circuit voltage tests:

• Note: Bleed surface charge before testing open-circuit battery voltage only if you feel surface charge has accumulated.
  • If the car has been driven or the battery has recently been charged, surface charges will sway voltage readings
• To remove excess surface charge
  • Allow the battery to sit for 2 to 3 hours before testing
  • Or, turn the high beams on for 5 minutes & then wait 5 minutes more with the ignition off before testing
  • Or, apply a 15 second load of 1/2 the battery's cold-cranking amperage & then wait 5 minutes before testing

How to load the battery for so-called closed-circuit tests:

• Note: Apparently, you test the battery voltage while under this load! (correct me if I'm wrong!)
• Always fully charge the battery first (as a discharged battery will always test bad)
  • Apply a 15 amp load for fifteen seconds before testing (turn the high beams on for 1 minute with the ignition off)
  • Or, apply a 200 amp load for one minute (as stipulated in the Bentleys ... where you get a 200 amp load, I don't know)
• Test the closed-circuit voltage while the battery is still under this load!
  • Note: I'm assuming you test under the load (and not after the load is released); but the Bentleys are confusing to me on this point!

How to load the alternator at engine idle for alternator output tests:

• Note: Alternator output should be tested with the engine idling under the following four loads after at least 15 seconds of idling (for the alternator to ramp up):
  • Turn the high beams on
  • And, turn the rear defroster on
  • And, turn the fan on (full force, I guess)
  • And, turn the wipers on (to the regular setting, I guess)
• These loads should be left on while the alternator output tests are being performed.

I repeat: I am 'guessing' here (because the Bentleys confuse me to no end on the topic of loading).

It's as good as I can do ... so ... PLEASE (pretty please) someone who actually knows the answer ... please correct and clarify the loading/bleeding/running situation as needed!

Thanks.

As always, I appreciate your efforts Blue.

Here's an update, that has raised more questions. I decided to remove the battery disconnect, just as a possible variable.

So I do so, drive the car for a few minutes, repeat test -- heads on for one minute, engine off -- and now I'm getting 12.1V. ?? Any ideas why this would make a difference?

I'll keep watching it daily.

Originally Posted by Edgy36-39

and now I'm getting 12.1V. ?? Any ideas why this would make a difference?

I don't have a clue so I hope someone else offers their advice. Sorry.

Today, I laboriously pulled my BMW battery out of the compartment (some pictures are posted here):
- Good Replacement Batteries for the e39?

Again, it was taking more than 6 amps for a long time (maybe a half hour to 45 minutes), which I think is what blew out my entire instrument cluster:
- Warning: I charged my battery today & apparently killed my instrument cluster & MID



I peeled the two stickers off & pried up the six caps (I'm not sure 'how' you can remove them without causing damage to the flimsy rubbery plastic edges) and added fluid as needed.




Most cells took 15ml of distilled water, but, cell #4 (counting #1 as the one closest to the negative terminal) took 60ml, cell #5 took 20ml, and cell #6 took 30ml. Cell #2, which contained the specific gravity hydrometer was showing as 'green'.

BTW, what do you guys use for specific gravity test tools?

NOTE: I asked that as a separate thread, just now, over here:
- What tool do most of you use to test the specific gravity (hydrometer) of the battery

On the same topic of testing battery & alternator, I just purchased the "Car Voltmeter"; basically a Voltmeter that you simply plug into the cigarette socket and read.

1. Battery Voltage (for BMW key out of ignition; for Honda etc. you may need key in position II but engine OFF. It all depends on the car design of the cig socket circuit).

2. Alternator Voltage (engine running).

I got "Vector VEC008" model on ebay for $10/each. I keep it in the glove box and it is a fantastic device that allows you to check the state of your battery and alternator without leaving the cockpit! Highly recommended for any vehicles that you own.

Here is a photo of the "Car Voltmeter":

Is there anyway for me to check if my alternator is bad without actually starting the car? As some of you might know, my car fires up but dies after a second or 2. Or is the only way to check is to remove the alternator and bring it into autozone?

Originally Posted by ill_kuma

Is there anyway for me to check if my alternator is bad without actually starting the car?

When I brought mine to Autozone, they put it on a machine which spun it to test it ... so 'most' of the tests certainly need it to be spinning.

I 'suspect' you 'can' test continuity, bearing noise, and voltage regulator & diode integrity on the vehicle without the engine running ... but we'd need someone to tell us which test points to use and what values to expect.

FYI
people said this Equus 3721 is no good, the battery voltage is reading low

I bought US made

http://www.amazon.com/gp/product/B0043G1FZG



A bit more expensive but looks like more quality staff

Patent pending technology that virtually eliminates unexpected car battery failures
Alarms sound and error messages flash long before your battery reaches its end of life
Monitors the battery 24/7, watches the battery when the engine is started, detects alternator over & undercharging conditions
Displays battery charge state, engine start time, engine start voltage (most cars), alternator/battery voltage
Designed to work in 12V power receptacles (cigarette lighter), no tools required

Cn90 -- have you unlocked your cluster? If you have, can you confirm if the readers your cluster gives you for same voltage reading as your new meter?

My cluster doesn't match testing done at battery itself, and I'm wondering if cig lighter tool would match.

Edgy,

I verified the $10 voltmeter shown above (Vector VEC008) with my trusted Digital Voltmeter and it matches perfectly.

Originally Posted by cn90

I verified the $10 voltmeter shown above (Vector VEC008) with my trusted Digital Voltmeter and it matches perfectly.

My cluster readout well matches my Fluke 75 within reason.

I wonder what they use for a 'voltmeter' sensor in the cluster?

Where actually is the E39 voltmeter located anyway? In the DME?

BTW, this thread shows the importance of the battery to healthy E39 electronics:
- Case study: Low-voltage dead instrument cluster - no alphanumerics & most gauges inop

Here are, from that thread, the easy-to-do steps for testing battery voltage after charging:

1. The charger open-circuit voltage is about 12½ volts DC RMS with the battery out of the loop.
An oscilloscope previously revealed the charger puts out roughly about 14 volts peak to peak full-wave-rectified at 120Hz; but a DMM only measures RMS voltage ... which, in reality, is all that the battery cares about anyway.)



2. The charger closed circuit voltage, in parallel with that of the battery, is about 13¼ volts DC.


3. The battery alone, without the charger, is about 11½ volts (after being charged for 12 hours).


4. The charge current (after 12 hours on the charger) is reading on the Fluke 75 DMM just about what the gauge on the charger is reading, at about 2 ½ amps (so I think the gauge on the charger is reasonably accurate).

Doing a search today to find better techniques to find parasitic leaks, I happened upon this novel (to me) voltage-drop method described in this thread:
- E46 (1999 - 2006) > Battery dies when car not driven for 2 days or more

Originally Posted by chansta

Smart: But you would have to remove every fuse and connect the ammeter to find the bad circuit.

I would recommend having a separate DMM attached to your battery to also get a total amperage reading while you're doing the voltage drop tests (this way you can see the total amperage draw (AKA PARASITIC DRAW) drop to an acceptable level as you pull the one fuse with the excessive voltage drop.

But, even smarter: Do a voltage drop over each fuse in the DMM mV setting (yes even a fuse will have a tiny voltage drop). This way you don't have to pull every fuse until you come to the one fuse with a voltage drop (which would indicate current flow within that circuit). This will save you time.

For the record, here are pictures of all the fuses in my E39, well annotated (here's just one picture):

[QUOTE=bluebee;5825221]For reference, if someone comes here for a system reboot, here is how to properly do it (AFAIK) based on this thread.

Note 1: A full system reset procedure is as follows:
1. Pull down the battery access door in the trunk.
2. Remove the negative battery cable with a 10mm socket wrench
3. Remove the positive battery cable with a 10mm socket wrench
4. Touch battery cable terminals together (away from battery) for about 5 seconds (a small spark is said to be normal as this is said to be stored power draining from the system); on the E39, short with your wrench because the cables do not reach each other otherwise.
5. Allow cables to remain disconnected for about 5 minutes
6. Reconnect the positive battery cable
7. Reconnect the negative battery cable




Don't EVER, EVER do this! You need to used a fused circuit between those terminals.
Why? Because many components on these cars (especially e-60 and newer) have huge amounts of capacitance built into them. If there is a failure anywhere along the line, you just fried something.
Always use a small wire with a 5 amp fuse.
And if you don't think that's important, I have a few people that will disagree with you after damaging things first hand.