Yeah, I've been wondering about that. I live in the Phoenix area and the engine fan kicks in and runs all time after I shut my car off. My battery just died a month ago. It was only a year and nine months old. I was wondering how much juice the electric fans draw.

Also, I have my iPod connected in my car and it doesn't seemed to be on switched power as it looks like it is being charged after I turn off my car.

I should invest in a trickle chargers as you have.

 

I use the same battery tester and can tell you that if you load the battery for a full 10 seconds and the indicator stays in the range you show, the battery is good. What the service adviser told you about locking the car does not sound right. I can't say for sure, but I think that there is less drain when the car is unlocked because all systems shut down when it is unlocked, even the motion detecting security system. This is not the case when the car is locked as the security system continues to draw current from the battery.

You seem to have some troubleshooting abilities so I would suggest that if you have a decent volt-ohm meter you check the parasitic drain when the car is unlocked and everything is off. It takes a period of time for the electrical system to shut completely down after the ignition is turned off and the doors closed. Open the trunk and wait until the light times out. By the time it times out (1-2 hours) the electrical system will be asleep. Then disconnect the negative battery cable and connect the volt-ohm meter's black lead to the negative battery terminal, and the red lead to the cable that you removed. This completes the circuit and you can read the current drain. I'm pretty sure you want it to be in the 250-300 miliamp range (0.25-0.3amps). Assuming that you don't have a range finding VOM, be sure that you have the dial on the meter set to the correct AMP scale and the probes in the correct sockets before you connect it. If the meter goes over range, switch to the next higher scale until you get a reading. If it's much more than 300ma, find out from the dealer what the limit is so you can determine whether you have a problem. If it's 300ma or less, whatever caused the battery to go dead in a few days does not have to do with excessive current drain when the car is turned off. Off-hand I don't know the reserve capacity of the battery, but would expect it to be around 70 amp-hours. At a linear current drain of 300ma, it would take about 10 days to fully discharge. Longer if the current drain decreased as the battery voltage declined. Hope this helps.

 

When I ran such a test on my Mercedes, I found that for about 30 seconds the amp draw was higher and then it settled down to a much smaller load. I suspect that you will see something similar as I attribute some of the higher initial draw to some of the computers going through a boot cycle and basic systems checks. Then to sleep mode.

Good hunting.

 

I have a '08 C4S Cab. I was having trouble with the battery being sluggish on starting the car. I put 4K miles on it last year. My mechanic told me I should always lock the car even when it is the garage. Locking the car puts it into a "deeper sleep" which will have less of a draw on the battery. I use a battery tender during the winter months as I don't drive the car. I keep the car locked throughout the winter. Since I have been using this approach I have resolved my sluggish battery issue.

 

These cars WILL drain the battery if left unlocked in a garage over time, and even shorter periods of time if the battery is weak. CAN network communication still occurs with modules not in a sleep state without the lock command. No speculation, it happens.

 

The same kind of problem on my 12 997.2S Coupe was a bad module. The bad news is that it took the dealer nearly six months to find it and fix it!

Good Luck

 

+ 1 confirmed.

 

This is the BatteryMINDer I use.

 

Jason:

My 997.2 C2S daily driver has the same issue and is in fact sitting lifeless in my garage.

- I purchased my car 11 months ago under CPO.
- After having the car a few weeks the battery died - it went completely flat.
- Porsche Service came back with a NPF/NTF and attributed it the battery just being worn out - and I got stuck with the tab for a new battery.

She died again over the weekend... after ~ 10 months on a brand new factory battery. But this time I attribute the fault to the PCM.

- After jumping the car I noticed that the PCM did not boot up. I can hear the PCM try to boot, the lights flicker and then it reboots about every 10 seconds in a continual loop.

- After turning off the car and locking the car with the remote I can still hear the PCM trying to boot, even after being shut off and locked for several minutes.

She is going back into the dealer again today, but this time I am convinced it is the PCM causing the power drain. I drive the car regularly, the battery is new, I always lock it with the remote and I even go so far as to power down all the electronics before I lock it up. I am convinced that the 997.2 has a bug in the PCM causing a power down, this is not pilot error.

 

Is your car stock? No changes anywhere in the electric bus?

 

My 997.2 battery lasted 5 years- just replaced it last Oct and bought the car in September 2009 new. I don't drive it a ton 28000 miles in just over 5 years and no trickle charger or anything. This year I did a few 2+ week trips and I'm sure that contributed to a slightly earlier demise. Battery should last a good 5 years or you have a bug.

 

Why do you say that long road trip contributes to a battery demise?

 

sorry, I wasn't that clear. The car sat for 2-3 weeks while I was traveling by air to other parts of the world for business and pleasure 😀..

 

Got it, thanks!

997s use about 40mA idling, roughly 1Ah/day, 7Ah/week - 21Ah in 3 weeks, which is about 1/4 of a fully charged (80/90 Ah) battery.

 

Very interesting, thanks. How does ambient temperature affect that. I assume that cold weather is somehow harder for a battery.