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Old 09-17-2011, 02:34 PM
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bluebee bluebee is offline
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Location: San Jose, California
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Mein Auto: 02 BMW 525i M54 auto 130K
DIY how to test a BMW E39 battery & alternator

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 ...

  • 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@80F === fully charged (Note: May be up to 13.8V.)
    • >= 12.4V@80F === 75% charged
    • >= 12.2V@80F === 50% charged
    • >= 12.0V@80F === 25% charged
    • <= 11.7V@80F === 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@80F === OK
    • > 9.5V@60F ===OK
    • > 9.3V@40F ===OK
    • > 8.9V@20F ===OK
    • > 8.5V@0F ===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@80F 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) ( & 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
      • 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
    • 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)

Last edited by bluebee; 09-20-2011 at 09:49 PM. Reason: I will improve this DIY with whatever information others provide (so we can leverage it to others)
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