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Pelican Technical Article:
Battery Disconnect Switch / Battery Buddy Installation

Time: 1 hour
Tab: $150
Applicable Models:
986 Boxster (1997-04)
987 Boxster (2005-08)
Parts Required:
New battery, trickle charger
Hot Tip:
Check your battery before it leaves you stranded
Performance Gain:
Reliable starting
Complementary Modification:
Install trickle charger

  This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your Porsche Boxster.  The book contains 312 pages of full color projects detailing everything from performance mods to changing your brake pads.   With more than 950+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Boxster owner's collection. The book is currently available and in stock now. See The Official Book Website for more details.

Check out some other sample projects from the book: 

Need to buy parts for this project? Click here to order!
     At one time or another, everyone may have problems starting their Boxster. The first place to look for trouble in your starting system is your battery. The battery is perhaps the most important electrical component on the car, and due to its design and nature, is perhaps one of the most troublesome. Before doing anything drastic like replacing your starter or looking at your fuel injection ECU, you should make sure that your battery is in good condition.

     Begin by checking the voltage on the battery posts using a voltmeter. Place the meter's probes on the posts of the battery, not the clamps. This will give the most accurate indication of the voltage in the battery. A normal battery should read a voltage slightly above 12 volts with the car sitting still, and no electrical devices on. (The small trunk light in the front trunk shouldn't make a difference in the voltage reading.) A typical reading would be in the 12.6-volt range when the battery is fully charged. If the reading is 12 volts or less, then the battery needs charging or needs to be replaced with a new one. To be certain, you can take your battery to your local auto parts store for testing.

     While older batteries often exhibited deteriorating performance prior to their failure, I recently had an original OEM BMW battery fail on me in my BMW 5-Series. The car was running perfectly fine: I had just driven about 350 miles the previous day, so it should have been well charged. The next morning, I got in the car, and it started fine. I drove about 3 miles and stopped off to pick something up. I shut off the car, and was inside 3 minutes at the most. When I got to the parking lot, the battery was completely dead. There was not even enough power left to open the power door locks. It did turn out to be a complete battery failure. I was surprised because I'd never had a battery fail like this before: it always seemed to give out slowly. Some of the informal research I've done since then seems to indicate that the newer technology used in these batteries tends to lead to this type of occasional failure.

     When the car is running, the alternator should be outputting anywhere from about 12.5 volts to about 14.5 volts. If you don't see any significant change in the voltage after you start up the car, then your alternator could be faulty. If the voltage is high at the battery (around 17 volts or higher), then the alternator's regulator is most likely faulty and needs to be replaced. Overcharging the battery at these higher levels may cause it to overflow and leak acid all over the inside of your car. See Project 82 for instructions on how to replace the alternator.

     Do not ever disconnect the battery ground strap from the battery while the car is running. The battery acts as an electrical capacitor and filter on the entire electrical system, and the car's electrical components expect it to be there, even if it doesn't hold a charge. Disconnecting the battery terminals while the engine is running can seriously damage the computers and systems of the car.

     Sometimes it may be necessary to reset the computers of the car, for example, to clear error codes. Some books recommend disconnecting both terminals of the battery and touching them together to empty all of the capacitors and stored electricity in the system. While this works, it can possibly create a quick electrical shock to the system. A trick I learned from Tony Callas of Callas Rennsport is instead to place a resistor across the two terminals, or simply use a diagnostic lamp that will act like a resistor. Doing this will slowly dissipate the electricity over a few seconds instead of all at once.

     Once you have determined that your battery is fine, you should make sure that your engine ground strap is properly installed. The engine and transmission are mounted to the chassis using rubber mounts. While great for the suspension, the rubber mounts make lousy electrical conductors. To compensate for this, there is an engine ground strap that electrically connects the transmission and engine assembly to the chassis, located inside the engine compartment (see Figure 1). Check the strap to make sure it's not corroded or damaged. Make sure that you clean both ends of the strap and the areas that it mounts to on the chassis. With all electrical connections, it's a good idea to clean the area that you are mounting to with rubbing alcohol, and also to sand the area lightly with some fine-grit sandpaper or a wire brush. Doing so will remove any dirt, grime, surface rust, or other corrosion that may interfere with creating a good electrical connection. While you're at it, clean up the battery terminals as well in a similar manner.

     If you have discovered that your battery is weak and needs replacement then you need to replace it. Follow the steps in the photos of this project. When purchasing a new battery, I recommend the newer-style sealed or “maintenance free” types. Sealed batteries may be more prone to damage when you deep cycle them (let them run all the way down), but require less preventative maintenance. Be sure to purchase a battery that has the same group number and CCA rating (Cold Cranking Amps). Check the freshness date on the battery that you are purchasing and avoid any batteries that are more than six months old.

     You disconnect the battery by disconnecting the negative, or ground lead from the battery. Always disconnect the negative or ground lead first: if you disconnect the positive / hot lead, there is a chance that your tool may touch the metal chassis. This will result in a short circuit which would be quite dangerous. The worst case scenario would probably be where your wrench hit the chassis, was instantly welded there by the current, and then the battery overheated and exploded, because you couldn't break the connection. In other words, be sure to disconnect the ground first.

     If your car has the original radio in it, be aware that you will need the radio code if you disconnect the battery. This code is typically included with the documentation / owners manual that came with the car. The Porsche dealer can look this code up for you if you don't have it, but that can be a huge pain, and most dealers will charge you for the service.

     Leaving your lights on in your car can seriously damage the battery. Automotive batteries are not typically deep cycle batteries, which means they do not like to be fully discharged. If you leave your lights on and drain your battery several times, then you will weaken it each time and have to replace it sooner than later. If you need to jump start your battery, then you should refer to the section in your Boxster's owner's manual. The procedure is very straightforward and very similar to other cars.

     The Boxster has a few power-saving stand-by modes that it will enter after certain periods of time. If the ignition key is removed, accessories such as the trunk lamp, interior lamp, radio, etc will be switched off automatically after approximately two hours. If the car is locked, then these will switch off after 10 minutes. If the car is not started or unlocked for more than 5 days (7 days on the 2005 and later models), then the remote control standby function is switched off, and you will need to unlock the car using the key.

     After you disconnect your battery, the DME computer will lose some of its history memory used for adapting the fuel injection system. As a result, the idle may fluctuate, and the fuel injection mixture may be slightly off as the car relearns its settings.

     Probably the best way to protect your battery from drain and damage is to install a trickle-charger / battery maintainer on it. This charger plugs into the wall when you are not using the car, and constantly monitors the battery, charging it as needed when the voltage runs down. Every car battery has internal electrical leakage that will cause it to become fully discharged over time if not properly maintained. A trickle charger can keep your battery fresh year-round, even if you don't drive the car for months at a time. Beware of cheap chargers though, as they can accidentally overcharge your battery, causing more harm than good. The trickle charger I like to use in all of my Porsches is the Battery Tender, available for $40-$60 at
The infamous drivetrain ground strap is one of the easiest parts on the car to overlook, yet it can cause so many electrical troubles.
Figure 1
The infamous drivetrain ground strap is one of the easiest parts on the car to overlook, yet it can cause so many electrical troubles. Since the transmission and engine are insulated by rubber mounts, the ground strap is the only significant ground to the engine. If the ground strap is disconnected or missing, then the current that turns the starter must travel through the engine harness or other small points of contact. When I was working on the project Boxster for this book, I forgot to install the ground strap. When I went to start the car, it wouldn't start, and instead, the current ran through the right side stainless steel brake lines and completely cooked the line. That was a new experience for me: don't forget your ground strap!
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The battery is located in the front trunk compartment on the Boxster.
Figure 2
The battery is located in the front trunk compartment on the Boxster. Turn the plastic tie-downs to remove the black plastic cover (yellow arrows).
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Always disconnect the black colored negative or ground connection first (green arrow) from the battery post (green arrow).
Figure 3
Always disconnect the black colored negative or ground connection first (green arrow) from the battery post (green arrow). If you are not planning on removing the battery, then this connection is all you need to disconnect: there is no need to disconnect the positive / hot lead to the battery. When you disconnect the ground from the battery, make sure that you place or tape the ground lead aside: you don't want it accidentally falling on the terminal of the battery while you're working and effectively connecting up the battery again. If you are replacing the battery, be sure to properly hook up the vent hose once you have installed it in place (blue arrow). The yellow arrow shows the wire for the Battery Tender harness. You can route it through the fire wall (see Photo 3 of Pelican Technical Article: Litronic Headlamp Kit Upgrade), or you can simply zip-tie it to the plastic mesh located on the right side.
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If you are removing the battery, then simply loosen and remove the hold-down clamp that attaches the battery to the chassis (yellow arrow).
Figure 4
If you are removing the battery, then simply loosen and remove the hold-down clamp that attaches the battery to the chassis (yellow arrow). Stand inside the trunk and lift the battery out of the car from there (they are quite heavy). The inset in the upper left hand corner shows the permanent attachment of the Battery Tender cable to the negative lead. A handy device I like to install on all my cars is a battery cutoff switch (lower inset). Installation of this switch on the battery ground allows you to remove the green knob and shut off all power to the car. An added tip: connect a small inline fuse from one end to the other, and a small amount of current will continue to flow, keeping your radio and DME from being cleared out when the battery is disconnected.
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Whenever I pick up a new car, I almost always install one of these within the first few weeks.
Figure 5
Whenever I pick up a new car, I almost always install one of these within the first few weeks. The Battery Tender is a necessary tool if you're not planning on driving your car everyday. It plugs into the wall and trickle-charges the battery so that it won't run down. Although the kit comes with alligator clips for temporary installations, I prefer to hard-wire the charger into the battery, and simply leave the charging unit in the bottom of the front trunk.
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See Bonus Photos
Bonus Photos
Looking for more photos? Click to see bonus pictures for this project.
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Comments and Suggestions:
Cider Comments: I'm setting up my trickle charger but leave my Boxster outside. Is there a way to pass the cables through the car in order to leave it securely locked overnight? Thanks for the amazing advise
June 10, 2014
  Followup from the Pelican Staff: If you attach the charger to the jump start terminals in engine compartment, you can run leads up through engine compartment, from below. - Nick at Pelican Parts  
boxter Comments: I have 1998 Porsche boxter key door lock remote wont work why thanks
April 2, 2014
  Followup from the Pelican Staff: Is the battery dead? - Nick at Pelican Parts  
B. Comments: Hi,
I have a 01' Boxster S, putting in a new battery no reaction only a fan noise.
What did I miss?
March 31, 2014
  Followup from the Pelican Staff: I answered your first posting. - Nick at Pelican Parts  
B. Comments: Hi,
Got a new battery and there's a fan noise but, no reaction from the rest of the car. What's next?

March 31, 2014
  Followup from the Pelican Staff: if it won't crank, check that the starter is getting a start signal. If not. check the DME for fault codes. - Nick at Pelican Parts  
Pete Comments: Winter was not kind to my 02 Boxter. Had a trickle charger on so I thought, over the cold winter. Battery was dead yesterday. Boosted it, radio is now locked. Drove it for 30 mins, would not start after shut off. ?'s are, where can I find the radio code, and should I invest in a new battery?
March 24, 2014
  Followup from the Pelican Staff: Sounds like the battery is faulty. A Porsche dealer can get you the code. - Nick at Pelican Parts  
Moe Comments: No Lights came on in the dash nor does it crank over. The next day, the battery was drained. I did some trouble shooting and found out I mad a silly mistake. The battery cables were placed in reverse. The batter was drained. So I am recharging it and hopefully, it should crank over. All the fuses are intact. Thanks.
February 27, 2014
  Followup from the Pelican Staff: Thanks for the follow up. We appreciate it.

- Nick at Pelican Parts
Moe Comments: I installed a new Battery on my 2001 Porsche Boxster. I am unable to start the car. I can put the head light on.Do I have to reset something. I check the fuses. They look good.Please help.
February 23, 2014
  Followup from the Pelican Staff: Does the vehicle crank? Does the instrument cluster light up? I the check engine light ON with the key in the ON position? - Nick at Pelican Parts  
GREG Comments: boxster will only idea after battery replacement...any ideas? HELP!
January 18, 2014
  Followup from the Pelican Staff: Is the alternator charging? I would perform a charging system test. - Nick at Pelican Parts  
jeffd Comments: i disconnected my battery and now my radio is dead. The Porsche garage where I go tried to re activate the radio by putting in the code but they called me telling me they now have a message the radio needs to be repaired... Really, is that possible or do they have to reset the computer?
December 13, 2013
  Followup from the Pelican Staff: It is possible. The radio may have failed from a voltage spike or coincidence. - Nick at Pelican Parts  
Judicutie Comments: I plan to buy your book; am excited there is such a book. Right now this is my issue. I have 1999 Boxster Tiptronic. For the past few weeks it has been difficult to get the gear shift to press down far enough to get out of park. I've had to press and press to seemingly get it in the exact position. This only happens in park. It moves perfectly in all other gears right word?. I don't know if this is related as I haven't started the car in 3 days, but I opened the door tonight and there were no lights except the one on the radio and, of course, the car made no sound when I tried to start it. I could have left a light on 3 days ago. I have an Interstate battery I've driven for approx 20K miles. Ideas? Oh, and a few weeks before I had the gear shift problem, my doors stopped opening w/clicker battery in clicker fine, checked 2 diff places and the front and back trunks boots and bonnets? idk the terminology open sporadically. Can all of this be connected? Help!.
September 28, 2013
  Followup from the Pelican Staff: If your battery is discharged, i would start by replacing it. The issue with your shifter may be related to the shift interlock system. The interlock system may not releasing the shifter. - Nick at Pelican Parts  
Jose Comments: I fitted a switch to enable the battery, as I do not use the car every day and the battery keeps going flat, unfortunately I locked the bonnet. We Me and the AA man tried the put some power into fuse C3 but no good - what can I do?
March 24, 2013
  Followup from the Pelican Staff: There is an emergency release cable you can use to open it. Remove the right front wheel well liner. There should be a silver cable with a l;oop on the end. Pulling this cable should release the hood. - Nick at Pelican Parts  
Knocker Comments: I have disconnected the battery on my Boxster and shut the bonnet by mistake! Any ideas how to get in there now please?
November 1, 2012
  Followup from the Pelican Staff: If you can get to the engine compartment via the emergency release cable in left rear fender. You can connect jumper wires to the jump start points and open the vehicle that way. - Nick at Pelican Parts  
James Comments: For Figure 4, regarding the inline fuse tip. What amp rating would you suggest on the inlife fuse does it matter? Not an electronics expert but wouldn't that defeat the purpose of the Battery Cuttoff Switch if you connect the inline fuse fuse from one end to the other?

Would it possible/better to connect a small secondary battery such as 9V Battery or small 12v motorcycle battery to 996/986 to preserve the radios setting and DME?
November 3, 2011
  Followup from the Pelican Staff: Yes and no. The switch will prevent the car from being started, and also prevent a big short circuit from occurring if you short something out. The fuse can be as simple as a 1-amp fuse. In terms of preventing battery drain, you're right. Connecting the small fuse *will* not stop battery drain from happening - one of the reasons why I like the Battery Tenders. - Wayne at Pelican Parts  
Ray Comments: When I disconnect the battery lead the alarm goes off, it stops if I reconnect the battery, I'm removing the door trim to get at the window winder and want to disconnect the battery in order to remove the airbag.
April 1, 2011
  Followup from the Pelican Staff: Hmm, this makes no sense to me, when you disconnect the battery, the alarm *must* stop, if it's a factory alarm? Can you give more details? I'll copy this question to the forums so that you can reply there. - Wayne at Pelican Parts  
BobB Comments: Question/Comment: I always disconnect my Neg. terminal on my 1998 Boxster, in order to save the battery and avoid lock-outs. This morning for the first time, the car doesn't make a sound when I put the key in the ignition and engage the clutch. The battery is new and tests out at a full 14V. Any ideas as to what it might be...? TY. Bob B
March 14, 2011
  Followup from the Pelican Staff: Check out my article on adding the Battery Buddy to your car - it's far better to do this than disconnecting the battery. Every time you disconnect the battery, you force the car to "relearn" the sensors and fuel injection settings. Not terribly good for performance. The article on installing a Battery Buddy is right here: As for your particular problem, this happened to me the other day. There is probably corrosion built up on the terminals of either the battery or the cable. Get a wire brush and sand off the edges of both - that will probably solve your issue. - Wayne at Pelican Parts  

Check out some other sample projects from the book: 


Got more questions?  Join us in our Boxster / Cayman Technical Forum Message Board or our Carrera 996 / 997 Technical Forum Message Board and ask a question to one of our many automotive experts.

Or, see what other questions readers have asked about this article...
  Applies to: 1997 Boxster, 1998 Boxster, 1999 Boxster, 2000 Boxster, 2001 Boxster, 2002 Boxster, 2003 Boxster, 2004 Boxster, 2005 Boxster, 2006 Boxster, 2007 Boxster, 2008 Boxster, 1999 Carrera, 1999 996, 2000 Carrera, 2000 996, 2001 Carrera, 2001 996, 2002 Carrera, 2002 996, 2003 Carrera, 2003 996, 2004 Carrera, 2004 996, 2005 Carrera, 2005 997, 2006 Carrera, 2006 997, 2007 Carrera, 2007 996, 2008 Carrera, 2008 997
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