Battery discharge, dead, drained

OK...I've searched a few threads looking for this and found nothing but recommendations for a tender

My 348 has been sitting in my garage for the winter, warm and cozy. I've started it on occasion to keep things lubricated and to hear the music. Generally its been left alone for 1 or 2 weeks at a time without starting. At one point it went nearly a month. There has never been a problem. She rolled and started immediately every time. Last Thursday we had a rash of beautiful weather that caused me to take her out for the day. We cruised a total of about 120 miles. I pulled the top and enjoyed every minute. After re-aquainting myself with the majesty of her, I sadly put her back in the garage to wait for the next moment.

Today was that day. I rushed home from work with the knowledge I would be handsomely rewarded. Pulled the car cover sank into the seat turned the key and....nothing. No dash lights, no seatbelt mouse, nothing. The battery was stone dead. I put the charger on her and let it run at low and high amps for a while. Later, after it was nearly to cold for a top off cruise, I turned the key and she sprang to life. I let her warm and idle for a while to reset the codes. We went for a short spin to make sure everything was fine. dash lights we all extiguished at idle, battery light came on at 2000 RPM followed by check engine lights. A few miles and revs later, the lights went out (indicating the battery was now fully charged) and everything was fine.

Now the question

What could be the cause for the battery to go stone dead after only 5 days when it worked effortlessly the entire winter? What systems should I investigate to make sure they are NOT drawing when the key is off? How do I isolate systems to find the culprit? What could I have turned on during my drive last Thursday that won't shut off.

 

Put your ampmeter onto your main battery cable connection (in-line). If you aren't comfortable with this step, most independent mechanics will only charge you a half hour of labor to do it for you.

Note the current draw when your car is idling. Note the current draw when your motor is turned off.

Now begin pulling out the relays from your passenger foot panel. Pull a few relays and check the current draw. Continue until you find one relay that when disconnected, really drops the observed current draw.

Presto!

You've just isolated the circuit (e.g. car radio, aftermarket alarm, interior lights, front driving lights) that was draining your battery. At that point it should be child's play to figure out a proper solution.

 

I knew it would be you...Thanks. Now it time for a new multimeter

(justification is everything)

 

That's cool, but skip the idling current measurement test if you use a multimeter.

Turn the car off, disconnect the positive battery cable, insert your multimeter between the battery and cable, write down the current draw...then pull the relays.

When finished, disconnect the multimeter and reconnect the battery cable to the battery to start the car.

 

First thing

If you drove your car only for a short period and your battery light went out that does not mean you have a fully charged battery, all it means is that it charged it back up enough to show that it has some volts.

You should take your battery to a depot and have it tested under load, you might have one with a cell that is bad this would cause you some grief as it will not fully charge ever, if all is ok have them fully charge your battery I think yours is pretty weak, quite possible that your alternator might not be supplying full amps as well.

This is a common problem in most Porsches they will drain the battery over a short period of time, the only thing is using a trickle charger or turn off your battery switch.

In case you do use a trickle charger make sure you get a new battery or fully charge your old one before use.

 

Should I get in the habit of using a battery tender? I have one (came with the car) but I've never bothered to use it, since I've been driving the car every week.

- Eric

 

how old is the battery,,,, may be it just went flat.
I'd check the easy crap first..... pull the battery take it to the auto
store and have them check it before thinking something went south
on the car????

 

In your case no I would not if you drive it every week that is more than sufficient to keep everything charged, but if you go longer say 3 or 4 I would, never hurts the battery and you wont be left disappointed on a beautiful day, no offence Saint..

 

This is great, just checked starting mine yesterday.
wounldn't you know it... dead, i mean really dead.....
1.6 volts at the terminals.

now, how do you get that thing out of a rear installed
battery? let me guess you have to take the car apart, right?

 

It is a tight squeeze, but it can be removed from the top. Removing the cold air intake tube at the air filter box and the left tail light cover will provide extra room and does not require any tools to remove those items. You will need a 10mm socket with a long extender to remove the battery fastner. Thin gloves to help avoid bloody knuckles is also not a bad idea. The battery will need to be rotated along its axis as it is pulled up and then removed at an angle to clear the muffler heat shields.

 

Follow up

Put a charge on the battery. Drove it around. Did some real minor/preliminary inspections (terminal posts, tightness, etc...)
No problems found. Car sat for 3 days untouched. tried it today, started just fine. Problem solved.

I still have no idea what happened or why the battery drained. Maybe Lil Bastage was playing in the car. Time to set up a security cam

 

much thanks! I'll try taking the battery out from the top,