Why was my battery dead?

[Bob Sacamano]

Coincidentally, my S3 ('87) is in my garage right now, wheels off, up on stands. My battery wasn't draining (I do drive it very infrequently), but system voltage was too low, especially with wipers, lights, defroster on, etc. Battery is nearly new, and alternator is to spec.

First thing I did was check the battery cables and connections in the trunk. Terminals on the cables looked OK, but I cleaned and retightened them. Ground cable connection to the trunk floor was removed, wire brushed to be shiny, new washers, and a new bolt were used.

Next, I pulled the ground strap off the bottom right side of the engine, and these connections looked weak from the start. Same as in the trunk, everything wirebrushed to shiny, new washers, new nuts.

Third, ran a new 8ga. cable from the B+ of the alternator to the cable junction on the left inner fender. Again, all terminals cleaned, new washers, new nuts.

Finally, another (this one non-original) 8ga. cable run from the B+ of the alternator to the B+ of the starter motor, with all those starter connections also cleaned.

Now I've got just over 14.5V everywhere in the system, and for the minimal cost involved, this is a big improvement over the previous situation.

[andytitterton]

This may not help this particular thread, but it is the probable cause for my battery going flat - Check the timer relay for the interior lights. My interior lights are switched to the off position, but my battery appears to have been drained over several days due to the rubber seal around the door preventing the switch from being correctly operated when the door is shut. This results in the timer relay being permanently energised. This may only draw 200 milliamps (one fifth of an amp), but if you work it out, a 40 Amphour battery would in theory be flattened in 200 hours - say nine days. (40 Amphour = 40 Amps for 1 hour or 1 Amp for 40 hours, so 0.2 x 40 = 200).

This fault is something that wouldn't be a problem if the car is used every day. However, if the car is only used occasionally.........

[DavidH]

Here's what we did last week to make the electrons move better. First, we removed the negative battery cable, cleaned its contacts with sandpaper, and replaced it. Did the same with the braided ground strap between the engine block and the frame (one greasy mess -- used mineral spirits to remove the grease and used a Dremel tool and little sanding wheel to clean the contacts on the strap, the engine block and the frame). We then tested the voltage at the battery and found it to be over 14 volts at the battery at 3K rpm. This indicates the battery now is getting sufficient voltage to charge while driving. Unfortunately, we didnt take baseline readings before doing all this; so we werent absolutely sure we improved anything at all. But we think we did and that counts for an awful lot. We considered adding an additional wire from the alternator to the junction box (per many recommendations), but just couldn't fit our ham hands down to the back of the alternator. And since it was dinner time and we were dirty and tired, we saved that for another time.

[Bob Sacamano]

Just takes a few minutes to remove the air cleaner assembly, which will grant easy access to the alternator. Be sure to disconnect the battery from the circuit before going anywhere near the terminals on the alternator or junction block. Touch a wrench between either of those two things and just about anything else in the engine bay, and you'll be arc welding.