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Porsche 911 Carrera Battery Replacement and Trickle Charger Installation

Pelican Technical Article:

Porsche 911 Carrera Battery Replacement and Trickle Charger Installation


1 hour1 hr







Applicable Models:

Porsche 996 Carrera models (1999-05)
Porsche 996 Turbo, GT2, GT3 (2001-05)
Porsche 997 Carrera models (2005-08)
Porsche 997 Turbo, GT2, GT3 (2007-08)

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

Sooner or later, everyone will have problems starting their 911. 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, it 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 three 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 the unconnected terminals 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. It's located on the right side behind the rear wheel (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 and 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 owner's manual. The procedure is very straightforward and very similar to other cars.

The Carrera 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 my project Boxster for one of my other books, 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!

The battery is located in the front trunk compartment on the Carrera.
Figure 2

The battery is located in the front trunk compartment on the Carrera. Turn the plastic tie-downs to remove the black plastic cover (yellow arrows).

Always disconnect the black colored negative or ground connection first from the battery post (green arrow).
Figure 3

Always disconnect the black colored negative or ground connection first 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 Figure 3 of Pelican Technical Article: Installing Litronic Headlamps on the Porsche 911 Carrera), or you can simply zip-tie it to the plastic mesh located on the right side.

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.

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.

Comments and Suggestions:
911/996 Comments: My 1999 Carrera battery died due to lack of driving, could not get hood open to recharge. Owner manual states pulling fuse box cover and find charger connection and connect jump box and that would provide power to relay to open hood, trunk and gas door could not find it so I connected trickle charger to cig lighter plug and was able to recharge battery but still can't get under hood or gas lid any suggestions??
February 18, 2018
Steve Comments: I remove the panels of both doors check speakers wired they were in place the unusual noise persistent with radio off or on the noises meek the doors panels to vibrate very strong for 30 seconds it is happening when you unlock the car open the door before you put the key an the ignition switck lots off Porsche people complain about this no one found solutions are anyone do research little more
February 11, 2018
  Followup from the Pelican Staff: hard to say without hearing the noise in person. I would check the latch to see if it is binding. - Nick at Pelican Parts  
Steve Comments: Unusual noise came from both doors speakers in my 911 Carreras 2007 when I open doors for 30 seconds before I start the car I have no code the car has only 30000 thousand miles I wonder if you give me any advices.
February 3, 2018
  Followup from the Pelican Staff: The speaker wiring may be loose. Inspect the speaker, wiring and door jamb harness. - Nick at Pelican Parts  
DC997s Comments: Re Chris's problem with a hard to restart a hot engine. I have a 2005 911s with that problem. Replaced the battery and still had the problem. Had it further diagnosed by measuring the voltage at the starter. Had to get the battery "hot" cable replaced that goes from the battery to the alternator and to the Starter. Problem is at the junction at the alternator but you need to replace the whole thing. Unfortunately the extended low voltage at the starter causes the starter to pull more current and cause the windings to overheat and to bind up inside. Replaced the starter as well. So if you have this issue, check out the cranking voltage before replacing the battery and if the cable is faulty consider doing the starter at the same time.
August 13, 2017
  Followup from the Pelican Staff: Thanks for the input on this one. We appreciate the help.
- Nick at Pelican Parts
shmelvin Comments: I used a Ctek 8 step charger on a Boxster and a Q7 plugged into the power port is there an issue doing this on a 2002 911 C4?
June 27, 2017
  Followup from the Pelican Staff: Check with the charger manufacturer. backfeeding voltage that way could be an issue if the circuit is powered off when the ignition is off. - Nick at Pelican Parts  
youstacoach Comments: I have a 2002 996 that quit starting just clicked.. Pulled starter, took to starter repair shop. Fired right up. Said nothing wrong. Checked battery, good. Put starter back part way tried again. Clicked! Checked ground. Put back together. Going to take to dealer Tried again and started right up! Drove 4 more times went out to go home and CLICK! Anyone else have this problem? Suggestions?
March 12, 2017
  Followup from the Pelican Staff: Sounds like a connection issue. Possible battery cable or connection on a cable. i would voltage drop test the battery cables and connections.- Nick at Pelican Parts  
Sukhi Comments: Can you trickle charge a battery while its still connected to the vehicle? I charge my car every couple weeks because it dosent get used very often and always disconnect the battery before connecting the charger overnight. Seeing as you guys hardwire the chargers in permanently great idea which I may now do too it sounds like you don't need to disconnect the battery from the car first..?
February 26, 2017
  Followup from the Pelican Staff: It is safe to connect a trickle charger that is automatically controlled based upon the battery state of charge. - Casey at Pelican Parts  
Kirk Comments: true that disconnecting the negative ground is a superior way of preserving the battery for prolonged periods 6 months vs Charge-o-matic II?
December 7, 2016
  Followup from the Pelican Staff: Disconnecting the ground is a great way to preserve the battery. it may still require periodic charging. - Nick at Pelican Parts  
newbie Comments: thanks, decided to bypass factory alarm.. then lights kept flashing into alarm... previous owner installed an aftermarket alarm, poorly wired into ignition switch which became faulty, cut it out. all is good!
September 23, 2016
  Followup from the Pelican Staff: Thanks for the follow up. We appreciate it.
- Nick at Pelican Parts
newbie Comments: 1987 carrera 911, let the battery drain by accident, recharging and reconnecting battery, alarm goes off. alarm key was already switched to deactivate.. how do I get it to stop?
September 20, 2016
  Followup from the Pelican Staff: turn ignition on or lock and unlock driver door a couple of times. - Nick at Pelican Parts  
ClintS Comments: I have a 2001 996 Turbo and want to use the Porsche Charge O Mat with the cigarette lighter plug but want to know how the charger back feeds to the battery if the cigarette lighter won't work unless the key is in the ON position.
July 9, 2016
  Followup from the Pelican Staff: It won't. I would suggest a charger that goes to the battery. - Nick at Pelican Parts  
Jw Comments: Apparently the reason my alarm goes off every time I try to remove the neg terminal is not because the alarm is armed it wasn't but you have to have the key actually in the ignition and turned on.
June 3, 2016
  Followup from the Pelican Staff: Thanks for the follow up. We appreciate it.
- Nick at Pelican Parts
JW Comments: Went to replace the battery on my 911 but overtime I remove the negative terminal the alarm goes off!! How come?
May 26, 2016
  Followup from the Pelican Staff: The vehicle thinks it is being stolen. is the vehicle alarm disarmed before you begin? - Nick at Pelican Parts  
Robert Comments: Currently there's a 70amp battery in my 1998 Carrera. Seems a tad low for me. Would 74amps, or perhaps 77amps or even more be adviseable?
May 24, 2016
  Followup from the Pelican Staff: I think your vehicle takes between a 70 and an 80, if talking about reserve capacity. 80 might be a good choice if you are concerned about discharge. - Nick at Pelican Parts  
964hans Comments: Use a proper stabilized DC power Supply set at approx. 13.5 Volts and capable of delivering 10 amps and plug it into the cigarette light. Be carefull with some battery chargers because they don't have a voltage limiter
March 15, 2016
  Followup from the Pelican Staff: I can't confirm this is good practice, but thanks for the info. - Nick at Pelican Parts  
David Comments: Greetings, is there a way to avoid possible radio code issues or loss of other settings when replacing the battery ? I have a 997.2
I've heard of in the past , little low voltage widgets that can be plugged into the cigarette light to maintain some current to save memories while batt is out .
Also are the Deltran Battery Tenders compatible with the Optima batteries ?
thanks in advance,
March 4, 2016
  Followup from the Pelican Staff: I don't use those items for a few reason. They can cause a surge if the door is opened, possible to blow a fuse is too much draw goes through the socket. Plus the chance of shorting cables. best to jst get the radio code. You should have it just in case. - Nick at Pelican Parts  
Sbrundle Comments: To confirm a question from 997, I also just bought a battery tender and it comes with the circle connectors so that I can quickly connect and disconnect the charger/maintainer and connect at the battery terminal bolts which hold on the clamps. I travel a lot and it can be weeks before I drive my 996 again. Is it ok to connect both the red and black to the appropriate terminals of my battery? It is not clear as the pictures do indicate above only the black connected to the ground terminal and where is the red lead connected? Also, a picture of the battery cutoff switch installed would be great! Lastly, is the ground strap behind the right wheel the entire tube like item shown with the bolt?
January 28, 2016
  Followup from the Pelican Staff: red and black can go to the battery. Just be sure the polarity is correct. - Nick at Pelican Parts  
Chris Comments: Looked at this for the Battery Tender recommendation but then the ground strap discussion caught my eye. Wondering if my ground strap could be causing an intermittent problem I am having with restarting my '04 996 C2 after a quick drive never any problems with the initial start. If I take it out for a 20 minute drive and shut it off for 5 minutes, about half the time it cranks very slowly or sometimes not at all when I try to restart it after that short break. The longer the break, the easier it starts up after. Ever run across this behavior?
January 17, 2016
  Followup from the Pelican Staff: Could be a battery cable. Best way to know is to voltage drop test the cables from the battery to the vehicle. - Nick at Pelican Parts  
Madmartin Comments: Hi , how long do you leave a trickle charger connected for ? I gave a 987 and the one I have connects to the cigarette lighter, and the plug part gas a red light on it . It's been connected for three days niw and the red light is off, should I disconnect it or leave it ?
Thanks Martin
January 1, 2016
  Followup from the Pelican Staff: Check with the instructions that came with your charger. I can't comment on it, without having experience with the specific model. - Nick at Pelican Parts  
yaknart33 Comments: A real easy foolproof way to discharge the capacitors in the electrical system is to pump the brake pedal 15/20 times .This is a standard procedure on a ford probe,works well and safely on most any vehicle.I am a retired Ford Senior Master Tech ,gas ,diesel,hybrid,lpg,cng ,34 years ford dealer experience.
December 21, 2015
  Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
jrs Comments: What battery tender should I buy for a 2008 911 Turbo?
December 10, 2015
  Followup from the Pelican Staff: the brand is called battery tender.

Give our parts specialists a call at 1-888-280-7799. - Nick at Pelican Parts
Mavrick Comments: There is a wire hood release for the front hood in the top of the front right wheel arch. Turning the wheel full crank will give you a liitle more room.
July 28, 2015
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it.
- Nick at Pelican Parts
Matt Comments: Super quick question - could a dodgy ground strap cook my voltage regulator? Or is it more likely to be a fault in the hot line?
June 24, 2015
  Followup from the Pelican Staff: Yes, a faulty ground could cause it to fail. - Nick at Pelican Parts  
997 Comments: Kind of an idiot question here. I've got a deltran battery tender with alligator clamps for my 997. What's the proper way to connect the clamps to the battery? Currently, I have the positive clamp connected to the positive battery post, and the negative clamp connected to a nearby bolt/ground on the chassis in the battery compartment. Should the negative clamp instead be connected to the negative terminal of the battery? Does it make any difference?
February 3, 2015
  Followup from the Pelican Staff: There are NO idiot questions!! This is actually a good question. If you leave the wires connected all the time it does not matter. If you connect the alligator leads to the battery each time you connect the charger it is safer to connect the Red clip to B+ first and then connect the black clip to a ground connection away from the battery in case of arcing, you don't want to ignite any gasses coming from the battery case. - Casey at Pelican Parts  
Wizard Comments: Would like to replace a dead battery on my 1999 996 cabriolet. Need to get front hood open first. Don't have the red posts in my fuse box. I heard of an emergency hood latch somewhere near the front end . Can any one help?
January 24, 2015
  Followup from the Pelican Staff: The emergency release is behind the left side of the rear bumper. Once the rear bumper is release, you can add a jump pack to the jump start points and power up the vehicle to open the front hood. - Nick at Pelican Parts  
franco Comments: Need to know the amperes that the 911 uses thankyou
October 29, 2014
  Followup from the Pelican Staff: What year and what part? - Nick at Pelican Parts  

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Page last updated: Wed 2/21/2018 02:41:51 AM