Cayman battery load when parked

There have been a host of complaints, opinions and misinformation regarding battery drain from the idle load of a parked Cayman . As most know by now, special instructions in the owners manual must be followed to "power-up" a Cayman with a dead battery in order to open the front boot and access the battery . Many of us use battery maintainers to keep the battery charged when our cars are parked for extended periods. But how much current drain does the Cayman place on the battery ? I decided to measure the actual battery load under different conditions and states in order to understand the true need for a battery maintainer and bring some facts to this subject. All of these measurements were taken on my 2007 Cayman S . I doubt that model year or optional equipment will make much difference in these numbers. For reference though, my CS includes the following options: Bi-Xenon's, PASM , Sports Chrono , Auto Climate Control and heated seats. There are two key things to take away from this data: 1. You should NOT leave the key in the ignition switch when you park your Cayman . It draws 1.7 amps (after time delay loads shutdown) with the key in the ignition switch. This is about 100 times the load when the key is removed - and enough to drain your battery within a couple of days! Note that if you listen carefully, you can hear multiple solenoids and/or relays energize when you insert the key without turning it. These things take a LOT of current. Note that 1.7A this is more current that the Boothe Design and Deltran battery maintainers can put out. So with the key in the ignition switch and one of these maintainers connected, your battery will still drain! 2. It does not matter whether or not you lock the doors when you leave the car in storage with the key removed. The idle current once everything (interior lights, dashboard, etc.) times out and shuts down is about 15 milliamps (0.015 amps) - independent of whether the doors are locked or not. A heathly and fully charged battery should be able to easily support this load for several weeks without problems. Here's a summary of the steps I took and the measurements using a high quality digital amp meter in series with the battery . Note that current readings vary up & down by a several 10's of milliamps when the various electronic systems are active, until they eventually time out and shutdown from lack of door lock, door switch and ignition activity. This is likely controlled by timers within the various electronic control modules and/or CAN bus commands to shutdown these systems. One thing that I have not measured (yet) is how much below the ~15mA level the load drops after 7 days idle time. This is when the Cayman shuts down the receiver for the remote key locking system. One can assume this load drops even further after the 7 day timeout. Amps Cayman state -------------------------------------------- 0.12 Car locked, boot & trunk closed 0.05 Same - after a few minutes (load timeout & shutdown?) 4 Unlock doors - interior lights turn on 4.8 Open drivers door 5.2 Sit in driver's seat & close the door 1.8 Lock doors - interior lights fade out 5 Insert key in ignition switch - interior lights still on 8.5 Turn ignition switch on without starting car 2 Ignition switch off but still in switch - after interior lights fade out 4.7 Remove key from ignition switch - interior lights back on 5 Place key back in ignition switch without turning - interior lights on 2.2 Key remaining in ignition switch, off, after interior lights fade off 1.9 Same - after instrument panel shuts down (odo, speedo, etc off) 4.7 Remove key from ignition switch - interior lights back on 1.1 Exit car and lock with key remote - interior lights faded off 0.1 Wait a couple minutes (more load timeout & shutdown?) 0.015 Approximately 20 minutes after locking car (and continuously for the next 24 hrs) ----- 0.015 Key removed, doors unlocked, after a few minutes and for the next hour ----- 1.7 A few minutes after placing key in ignition switch (without turning), and closing doors - interior lights have faded & other loads time out (and continuously for the next hour)

This is great stuff, and it should be in the FAQ, imo... Thank you! brad

That is great info. Is there anyway to measure the "health" of a fully charged battery and how much "effort" under different miles/speed driven to keep it healthy or fully charged?

Definitely good info. Answered a lot of my questions. Thanks! -Moto

One of the most valuable posts I've read. Thanks for that. Don't anybody tell the wife/husband that you don't actually have to drive the car 50 miles twice a week to keep the battery charged.

I concur and as an FYI after getting my car back I noticed the battery seemed a bit rundown so I put it on the battery tender and it took more than 24 hours to get it back up to a green reading.

I had searched for this very information within the last couple weeks and came up empty handed. Thank you so much for doing the work to obtain this data set for us. Now I can figure out if I can go with a lightweight battery or not. Fantastic!

Thanks for posting. I put my 07 CS on the tender because the roads have been raunchy for the last week in Denver. Tomorrow and Tuesday look like good days to get it out and run it, though. Your data is really helpful!

All of this is likely true, but my wife's CLS battery will die if the car isn't run for 2 weeks or so... and the battery is completely ok. I know this from personal experience. Even after one week, when you first get in the car, a warning will show "some personal conveniences may not be available" This means some of the power options may not work until after the car is running for a minute or two. This happens when stored in a garage, unlocked, no key, etc. Several mechanics have told me no to leave the CS locked in the garage for a week or more, but that's about it. I've once left it for a week, but on a maintainer, with no problem. The damn thing about the Benz is that none of the sockets are "hot" with the ignition off and the maintainer won't work unless I hook up directly to the battery .

Thank you for these very useful measurements. I just got my car a few weeks ago but bad weather has kept it off the road for stretches - I kept going out after 4 or 5 days and idling it for a while to make sure the battery didn't die (I'd read the horror stories of what this means). Now I'm only wondering how much drain there is with the car off listening to the Bose / PCM with the screen off. I tend to let my wife shop for whatever while I sit in the car and it's nerve wracking trying to see how long I can listen to the stereo and get away with it (also wish there was some way to keep it from timing out).

Fantastic post. I have a question on the line in red. Is the "0.1" figure a typo, or does the power consumption actually increase after waiting a few minutes? The listed stats indicate the consumption drops from 0.12 to 0.05, then jumps to 0.1 and then drops to 0.015.

Nice work! Any idea how much current a cell phone draws when charging?

Actually there are any number of things you can do that will temporarily raise the current drawn. The particular lines you are questioning have a whole series of events in between them which "re-awaken" about every system in the car. For example, I also found that even after the car is in a relatively "quite" mode drawing ~15mA, a simple lift of the drivers door handle (as if to open the door, but while the doors are locked) will awaken the electronic nannies (alarm and who knows what else). The current drain jumps up as high as 2.2A and then drops in a couple of steps back down to the 15mA level within less than a minute. Realize that modern automobiles have literally dozens of small microprocessors scattered throughout them - instrument panel, ECU (the biggest one), radio, door lock system, PSM, Bi-Xenon self-levelers, ... many of them communicate among themselves via the (multiple) CAN buses (or other busses, depending on model year and manufacturer). I'm more fluent with the 1999 era BMW 's - but that's a loonnnggg story for another day.

I did a quick measurement of the current drain with the CDR24 (base radio, non-Bose) on vs. off. As I recall it was surprisingly small - on the order of 20-50mA, but I didn't write it down. However the current will vary with volume levels (assuming a class AB power amplifier). Unless your wife is leaving you in the car longer than the time lapse between required bio-breaks and meals, you have nothing to worry about.

75mA is a rough swag (Scientific Wild ***'ed Guess). Cell phones have tiny batteries and are carefully designed for low power consumption in order to maximize battery life between charges. So the charging current can't be too high without overheating and degrading the battery. And my swag is assuming a relatively inefficient conversion to the lower voltage required by the phone itself.

L8Apx, Awesome experiment. Thanks for sharing. This is good stuff. Santa Fe, It's kind of tough because even a totally spent battery will measure near or at 12 volts while at rest (no load). It's the current delivery that becomes compromised. The best way to measure the 'health' of a battery is with a load tester. A load tester will measure voltage and then apply a large current draw to the battery. An unhealthy battery will drop significantly from it's no load voltage when the load is applied. A healthy battery will drop much less. If you are simply trying to measure the state of charge, I would say that less than 11 volts should be charged or started. A healthy fully charged battery will idle a 12.5 - 13.8 volts. I don't know this for sure, but I would guess that if you let the battery slip below 9 volts, it probably won't start your car.

Thank you for the load numbers - as can be seen, 1.7A would draw 40Ahr in one day if the load stayed at that rate, but you have commented that it does drop after a period of time - would you know what that period is, and what the load drops to ? I am a bit surprised that the locked and unlocked car will draw 15mA - I would expect that a locked car would have more security devices powered. Again, great to see the actual measured numbers

Great info. As a practical matter,I recently left my 07 CS parked outside,covered & locked for 9 days. It started fine at 40 degrees F.

My original post stated: 0.015 Approximately 20 minutes after locking car The doors, trunks, etc. are monitored all the time in order to turn on the cabin lights as well as for the alarm. Consequently there is no added current drain to have the car locked and alarm armed. The alarm function is integrated in to one of the many computer modules in our cars.

Hello, My Cayman S 2008 battery which had been connected with a tender seems to have lost its power. Is there anything I can do before having to replace it? thanks!

Speaking of mysterious battery drain: Just in case anyone is tempted to install the "Foglights as DRLs" mod $2 DRL lights solution for fog lights - ******** Discussion Forums read post #22, and think again!

I have a 2016 Cayman S that is parked where there is no power available and I only drive it a few times a month. I have resorted to using a Jackery 300 with a 4 amp charger/maintainer to try to keep the Porsche battery healthy. It uses half the Jackery up about twice a week just to keep it in a state of semi full charge! I'd like to get a cheap solar panel that wouldn't be a disaster if stolen to leave on the roof when parked outside in sunny weather. What wattage panel is needed to overcome the idle draw?

Let's do some math! (I know, not fun for others, but even buzzed, I'll do it!) Jackery 300 = 293 Wh of power. Half = 146.5 Wh Two weeks = 14*24 = 336 hours. Therefore, the car is drawing 146.5/336 = 0.436w = 436mW. That doesn't seem so bad overall. The solar panel really depends on where you are, and how much sun you get. If you only get "max" solar power for 1/4 of the day (6 hours) then you'd need a panel capable of about 2W. Fact is, a solar panel won't generate max power unless it's aimed directly at the sun, and in full sunlight (ie, not cloudy)... so you need to factor that into your desires. Looking at Amazon quickly, the first link is a 30W panel, which would likely be sufficient. Note, you still need the battery of the Jackery to supply that power "continuously" to the car, but as you can see, it won't take a lot, at least based on my drunk math, haha.

Math is more fun when you’re buzzed. Lets the intelligence molecules flow better due to decreased resistance of the brain waves. Now that you mention it, I think I’ll crack a cold one.

Haha you guys are funny. And thank you. But I may have been ambiguous and didn't describe the draw very well. It uses about 90% of the whole Jackery every week but I recharge the Jackery twice a week so it doesn't deep discharge. The max capacity of charge id guess is 85% since it's LIon has been used for four years with about 25 recharges. So the math might be 293*.9*.85 = 224 watt hours per week. I don't know how to calculate from there. But this beast is definitely a power hog and my dealer battery swap was $750 after failed attempts by third parties at recalibrating the computers for my old faded battery . Even the dealer messed up the recalibrations a few times! I made them keep it and test it and sure enough! Parking brake errors. So since then I would rather tax a lithium and keep the Bosch AGM happy. Speaking of recharge I'll follow your lead and dip into my Italian pilsner stash!

We forgot to adjust for the inverter inefficiency. Wonder what the additional multiple would be......

I'm definitely getting one of thosw suction cups panels I found on Amazon per your prod to stash in the car for occasional or emergency use knowing the power hog issues. Don't need the Jackery or the charger/tender they plug direct. Example: Amazon.com

987 cars don't need a battery calibration. My 2012 base goes 3 weeks + without drawing the battery down.

Sure, you can continue to do the math. I showed my work, so adjust as needed. That being said, even if you double the draw, you're only at 4W and the small panel I mentioned is 30W, so you're still well within the requirements of the idea. As for the draw, 500mA is pretty low overall. Again, doubled is 1A, which is not ideal for standby load, but isn't out of the question either. Overall, I don't think the draw you're seeing represents are a real problem, and the 30W panel is more than enough to keep the system charged. Of course, all of this is based on my buzzed-math, so feel free to check my work. I offer no warranty on it, haha!

The 987 don't have a computer controlled alternator ... so there is no battery reset needed or available. I'm trying to remember if you can register a battery in it, I can in my Cayenne finally (the Foxwell NT530 made that possible), I rather think not. The electronics generation are similar to the 2006 Cayenne I owned which also didn't support battery registration. Just saying.. I wonder what the dealer actually set...

Interesting. Computer controlled alternator . I learned the hard way according to my mechanic that when it detects the battery is really unhealthy/low it starts shutting down systems and the shut down can be the death of the systsm. Case in point my parking brake system. So any 981 owners who don't drive alot make sure to trickle from the wall or a lithium like I am.

How to properly park a 981

Since you are apparently unaware, electronic equipment like your Battery Tender generate heat when plugged in. It's very likely that keeping it on your leather seat will be a mistake because it can not only damage the leather but risk more serious damage should it malfunction.

The tender and battery actually sit on the floormat, photo was so it could be seen and kind of a joke. But I am well aware of the fire risk, praying the Jackery doesn't explode! The inverter is rated for 300w and it draws about 65 for this application.