E39 - Battery/Alternator

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Diary of a Second Hand 15 year old Beamer (Maintenance - Battery Drain included...,
BMW E39 520i year 2000 Engine 1995cc)
M Series.

fig. Boot - Rear Fuse Cluster

Battery (Continued)
As each day has gone by I was still finding a problem with the battery retaining its charge. I was having to recharge the battery each day, I ended up with two old batteries on a charging recycle and again I decided to do some more research. The first task was to see if I had the correct battery for the model of car.
I ended up replacing the battery, with an ideal specification of: 100Amp with a CC (Cranking or starting power) of cc960,, anything over 100 with a crank of 750cc battery is acceptable, unfortunately the battery only lasted me seven days from a fully charged battery and it may have lasted longer if I hadn't put the suspect fuse 4 back in. The battery required another full re-change and one of the recycle batteries filled in for the remainder of the day. I was now thinking it may be somthing to do with the Alternator against all other better judgment of further investigations. The alternator is a standard 90 Amp, and I was close to changing it for a 120 Amp, I decided to do some more research before going through another purchase route:

fig. New Battery 019 100 Amp
Purchased eBay Tanya Batteries £59.99
Dealership can cost can between:£100-£200+

Normal Battery (vary on performance and make - guidance only)

Average Standing Charge
Battery Fully Charged   Disconnected     12.65V
            Fully Discharged....................   11.86V
Running Charge
Battery Connected and Engine Running 13.5V to 13.92V

Alternator ...........................................14.2V (posts)

Battery Terminal 12.47V
Minimum 12.4V.............
Best 12.6V...........Ideal

- On this test the engine revs should be around the 1500rpm and the voltage should read less than 15.5V. If over the battery is over changed (this can be as bad as undercharged) Don't exceed 15.5V. You can rectify this initially by loading the circuit, by swithing on the heating system, radio etc., as long as the problem doesn' persist. Rule-of-thumb, if under 15.5V the battery is ok.

The Alternator has an external regulator or an internal regulator, either way if theses have 'gone' the Alternator may need to be replaced. Check first before committing to the outlay: The onboard computer
The other possibility is the ECU (this instructs the onboard computer of voltage) has 'gone' and requires checking, try resetting to factory status (see page 34 ECU).
A full field test may also be required, and all electrics should be turned on (not rear screen defrost as damage to heater elements may occur). Check the following: Alternator connections (safety; If engine is running, be careful of fan-ideally do this before engine start).
The battery should be reading above standing battery voltage around 12.5V, anything above .5V over is working normally and exceeds the battery is working well! 13.16V is good.

If below standing battery voltage -There could be 'Resistor Voltage Drop' there may be a positive or negative problem within the electrical circuit.
To test this, (as described above, load the system, turn on radio and other accessories, lights - however not the rear defrost as this can cause damage to heater elements) checking the negative side input using a multimeter.....

                1. Accessories on
                2. Engine Revs to 2000 rpm
                3. Positive (red) lead to battery
                4. Negative (black) lead to Alternator case

Checking Alternator

Statatory Checks:

Workshop/Diary - Battery/Alternator

Reading should be: -00.1
Revs fluctuate between 00.1 to 00.2/3
Should read 00.1 = NO Resistance = Good Alternator is OK

Place New Labels onto new battery
a) Date of Purchase
b) Company - Contact details
c) Warranty period
d) Battery Specification Amp/CC
e) Make copy of Invoice - Keep Safe

Use RED Tape to indicate POS Terminal