How Healthy is Your Battery? Diagnosing the Flat Battery, No Start or Battery Draw Problems on Your Porsche.
Good battery goes flat? – no power or weak power after overnight parking? Finding a draw on a battery that causes it to go flat or have very weak power after a relatively short period e.g., overnight parking, can be a real pain in the you know what! Finding the problem can be a long drawn out and frustrating process – often this can also be expensive because of the hours involved to establish the source of the problem.
Here’s what you need to know and some shortcuts to solving battery problems:
Primarily, you must make sure you have a healthy battery and a healthy alternator before you start trying to work out a bigger problem. A battery showing a 12V reading can be unhealthy! The key measure is the Cold Crank Amp performance or CCA – this is the power to start the car when snow is on the ground! Every battery has a CCA rating shown on the case.
The battery also shows the manufacturing date. Batteries start to decline in health rapidly after 5 years despite the amount of times the car is driven. In warm climates you may have a seven year old battery that is doing fine – just hold on, because at some point soon, the performance will fall off a cliff! The older the battery is, the more you need to test it as a maintenance precaution.
When the CCA declines, battery problems start to show up.
Notice the “Cold” in Cold Crank Amps – you can easily get through a warm summer with a battery that is low on CCA – less power is required to turn a warm engine. But, the first really cold and snowy day you rush out to start the car and head home, the battery will be flat! Just what you don’t need.
Most Porsche batteries are rated at 700 CCA or more. So, if you test a battery and read only say 550 CCA, the battery will perform OK (maybe slower crank) on nice hot summer days, but will definitely fail as the weather cools down. The cranking amps decline significantly as the temperature lowers, so it’s important to take into consideration the temp of the battery when you make the test. A battery in a warm and toasty garage might be OK. However, if you don’t factor in the temperature after the car sits outside on a cold day, you might be in for a surprise!
Low CCA is usually caused by a bad cell within the battery. Having a bad cell means the battery is also not capable of taking the charge from the alternator – so it will never recover. It will test at 12V – but that means nothing! From a maintenance stand point, test the battery in the fall to check CCA – then you’ll know if that no start flat battery is coming before it happens on a cold, snowy, dark night!
How About that Alternator?
Many folks are not aware that the car runs from the battery. The alternator simply charges the battery at a pre-defined rate while the engine is running. When you test the alternator, with the engine running just above idle rpm, you should see a 14.4V charge level. This level of charge will keep the battery healthy if the battery can accept the charge. If the alternator is outputting less than 13V or more than 15V, then the battery will not charge effectively and will become progressively weakened.
Alternators are pretty reliable on Porsche these days and the need to replace them is not that common.
The Battery Draw – How to Proceed
So, you have a good battery and a good alternator, yet overnight the battery goes weak and will not start the car in the morning. You may have enough power to light the dashboard etc., but the engine may not crank at the turn of the key or push of the start button. You have a battery draw.
Finding the component on an electrical circuit that is drawing power from the battery, requires isolating each circuit and the components on the circuit. First, if anything has been recently changed or installed, start there by disconnecting the item. Typical issues range from simple audio add-ons, to weird stuff like alcohol breath testers or oxygen supply devices!
Put a meter on the battery and establish the amp draw when the car is sitting. The car has two modes while parked – awake and asleep. The sleep mode will typically not kick in until approx 30 mins after the car was last touched. Each vehicle has a set amp draw for sleep mode based on accessories, but this should be a very low amp level and clearly different from the awake amp draw. At this stage, with a draw problem, you should see a sleep mode amp draw that is higher than normal.
Next, isolate circuits by pulling fuses. Note the amp draw before you pull the fuse and the change afterwards when the car goes into sleep mode. This should isolate the circuit that contains the problem. Now all you have to do is to work out which electrical consumer on the circuit is causing the problem!
The frustration here is caused by the fact that every time you make a change e.g., pull a fuse, the car will wake up and you have to wait 30 mins for the sleep mode to become active to see the amp change. Looking at the number of fuses and adding 30 mins to each to test, one can quickly see why this could be a long-drawn-out process. This is where you might want to call upon the skills of an independent Porsche repair shop where solid experience can reduce the time and frustration in finding a battery draw.
Short Cuts and Likely Problem Candidates
Most of the electrical systems on a Porsche are ground switched. This means they’ll usually have a wire that delivers a constant power supply via a fuse. The ground side of the circuit is completed from the device by some sort of switch, that enables the device to turn on and operate. This could be a physical switch, but more likely, an electronic switch via a control module. Some major power consumers use the same principal but across a relay. The relay closes by the ground side of the circuit being provided through a switch. The relay then delivers direct high power battery voltage to the consumer on demand. This means you can use relatively low voltage to signal and close a relay, while the relay delivers high power to the consumer. A battery draw from these high-power consumers is usually very obvious – for example, an hvac blower motor that runs permanently when the car is turned off or a radiator fan that runs constantly. You might have a bad relay or, on the other hand, a good relay that’s just simply doing what it’s told to do by a bad control module!
An electrical short inside a component can complete the ground circuit without needing an external switch to be in the “on” position – this enables the device to continually draw battery power. This could well mean the device functions perfectly normally when asked to, but that it simply does not turn off. So, don’t be surprised if the offending device causing a battery draw, seems to work normally on demand. A classic example of this type of failure is the backup camera seen on the Macan and Cayenne. Yes, it works in reverse, but it never turns off when you select drive – you can’t see that because the screen switches back to the control menu, despite the camera remaining on – this equals flat battery in the morning!
Shortcut the process by trying to eliminate the most likely offenders first.
Unless you’ve been driving on another planet for a while, you’ll know that water and electricity don’t tend to mix that well! On a ground switched circuit, water is excellent for providing the conductivity need to complete the circuit.
“My battery goes flat overnight and my drivers door wont lock.” Water can easily enter the vehicle and do untold amounts of damage. Many times this manifests itself in weird behavior with water inside control modules or a corroded ground point – brake lights staying on, random suspension faults, doors that show open when closed etc. Less obvious water damage occurs across the contacts inside an electrical connector or inside a door lock actuator, for example.
Check the likely places water could enter and do damage. These include:
- The trunk space in the Cayenne, Macan and Panamera (typically caused by blocked roof drains – see common problems)
- Under the drivers seat in a 911
- Behind the drivers seat in most Cabriolet models
- Tail light access on Cayenne, Macan and Panamera
- Inside the front driver side door
- The center console – this is usually caused by spilling a refreshing beverage!
Most Common Causes of Battery Draw on Porsche
- Parking lights
- Interior lights, glove box and trunk lights
- Backup Camera
- Audio Amplifier
- HVAC control unit or Screen
- Door lock actuators
- Switch panels on the driver door
- Interior power sockets – cigarette lighters
- Alarm system
- After-run cooling fans and radiator grill motor
Should You Use a Battery Maintainer?
If you drive your Porsche at least every few days, there should never be a need for a battery maintainer. On the other hand, if the car will sit untouched for more than 2 weeks, then we do recommend a battery maintainer as a good precaution. We are not fans of the maintainer that can be plugged into the cigarette lighter socket. We recommend you always attach a maintainer directly to the battery if possible.
The battery in your Porsche is a long term maintenance item and should be part of your maintenance plans to keep it healthy.