I have a MY88 S4. The battery is just a little over two years old. The car is driven at least 1 - 2 days per week. In the past three months I've had two episodes where the car was started without issue for a month or two and then I come out the next morning and it won't start. I still have interior lights, stereo, etc., but not enough power to crank.
I have read many of the threads where people have a parasitic drain and the battery is dead after just a few days of not driving. This is not the case with my car. I guess the safe bet is to start putting it on the trickle charger when I swap out cars. Any thoughts would be appreciated.
PS - I am NOT mechanically inclined, but have access to some 928 savvy folks.

 

Rule of thumb for any Battery, if it's not charging its discharging, for extended battery life always use a battery maintainer (smart) not trickle to keep batteries topped off when not in use.

As for your issue, first do a search here many threads on this issue, start with what doesn't work, sounds like something is staying on (stuck relay?). Only way to find the drain is to start testing each fused circuit and then the un fused ones.

 

I misspoke earlier, I actually have a CTEK maintainer, not a trickle charger. I also have a battery status indicator (red/yellow/green) that indicates the strength of the battery. I will start putting it back on the maintainer whenever I see it drop to yellow from now on. Thanks!

 

Keith--

If you have the CTEK handy, I wouldn't wait for the yellow indicator. Just plug it in when the car isn't being used and let the smarts in the 'smart charger' do their thing. No reason to let the battery drain and refill when it doesn't need to.

At the same time, figure out what's causing the no-start. If you can drive it OK and just park it for a day to find a no-start, the car isn't reliable enough to drive anywhere really. Problem needs to be solved; the maintainer will mask the symptoms, but is not a real solution.

 

Keith,

Plenty of threads on battery drain issues- all too prevalent on these cars. One of the better tips is to check the central electrics first thing in the morning and see if you can find a relay that is warmer than the others. you can also check each fuse for current flow.

First place to start is to place an ammeter in series with the battery earth strap then get the missus to lock the car, allow a few seconds for the alarm to engage and then check the ampage. Anything more than about 30mA you have a problem that needs solving. If you are seeing this problem regularly it suggests you may have a significant leakage rate.

I had one many years ago on my late S4. Could not find the problem so took it in to the main dealers- they found a live wire in the tailgate with chaffed insulation was earthing. How the hell they found it was beyond me.

Rgds

Fred

 

Dave, dr bob and Fred: thanks for all your advice. I will get with one of my local 928 buddies (probably Don here in Houston) when time permits to try and track this down. For now, I will keep it on the CTEK more often.

 

do you have an IR gun?
run the car, for a few miles
shut it off shoot the relay panel with the gun,
wait 20 mins,
then shoot the CE panel again any hot relay is grounds for inspection/ replacement

 

If it's an intermittent problem, you might check the ground strap. If it's bad (and they go bad inside the insulation where you can't see it) you could have enough flow to run the accessories, but not enough for the starter. It will pull the "no-start" no matter what the battery charge is like if the ground strap is bad. Roger has new ones, and they aren't expensive.

The next time you get a "no-start", a quick and dirty test for this is to run a (single) jumper cable from the negative post of the battery to the wingnut where the ground strap attaches.

 

Diagnose your drain. They aren't hard to find if the drain is coming from within a fused circuit. Disconnect the battery ground strap from the chassis and get your multimeter out. Move the probe to Amps. Set your multimeter to 200mA or so. Place one probe on the chassis ground point and the other to the disconnected ground strap end. Your draw should be somewhere within 20-30mA.

For chasing the draw, have a helper pull fuses one at a time while you observe the readout. You'll need to disconnect the passenger door plugs to do this of course.