Batteries & Charging

Disclaimer: The content of this document relates to the Porsche 993 (911 1995 to1998) I am not a professional automotive technician and some of the opinions expressed in this document are just that, opinions, therefore, please feel free to use this document at your own risk. Many times a lot can be learned by simply watching qualified professionals work on your 993

Battery Not Charging - The 993 for some reason lacks a voltmeter on the dash. It does include a battery light in the clock that is directly connected to the alternator.  When illuminated it indicates that the battery is not charging. My understanding is that the battery light is actually part of the charging system and if the bulb is blown out your alternator will not charge. For this reason, it may be advisable to observe that the light illuminates when first turning the ignition on before starting the engine and always check the bulb before digging deeper into an alternator not charging situation. I have never come across this issue however others suggest that if you have the clock out for servicing and run the vehicle you will run your battery down.

Battery Status & Charging -- The 993 likes a fully charged battery with a voltage of 12.7 ~12.6 volts at rest after the engine has been just turned off and can creep down to as low as 12V over an extended sit with the alarm energized. The system voltage should be between 13.5 ~14.2V volts with the engine running. Any lower and the alternator/voltage regulator are not doing their job, any higher and the voltage regulator is not working properly and the excessive voltage will start to fry electronic components. If the voltage when running is too low and before looking to deeply for the root cause make sure the alternator belt is tensioned properly as discussed on this page as it may be too loose and slipping.

On occasion, I have accidentally left the dome lights on in the car overnight necessitating the need for a battery charge. 

I had an inexpensive 1.5 amp float charger on hand and purchased a  cigarette lighter adapter cord for use in the car. Now on the occasions where a mishap results in a discharged battery, I simply plug the charger into the cigarette lighter close the door on the 12-volt wire, lock the car, the dome lights go out,  plug the charger into the wall, and in and 4 hours the car starts right up. Since the charging rate is very slow one does not have to worry about overheating the battery or any additional venting. A premade cord can be purchased from Amazon or eBay the

nicer ones have a light on the plug that illuminates when the plug has a positive connection to the lighter socket. The cigarette lighter socket on our cars is the older slightly larger style so to make a snug fit some put a rubber band or electrical tape around the lighter plug or one can make the neat solution discussed on this page.

The advantage of using the unswitched, constant-on cigarette lighter socket over a direct attachment to the battery in the frunk is that one need not bother opening

Direct Battery 
Attachment Adapter

and closing the frunk to attach or detach the charger. If one decides to use the battery-direct connection method the frunk lid needs to be closed on the charger cord to extinguish the frunk courtesy light. 

If one prefers to leave the frunk ajar when using a charger the lower latch capture lever needs to be pressed down with a screwdriver so the latch is in the locked position to extinguish the frunk light and the frunk release lever pulled before closing the frunk when done. 

With the direct battery attachment method, it is best to use the adapter that comes with most chargers vs using the alligator clips as the adapter makes for a positive connection where the clips can inadvertently slip off, and when live, touch things they shouldn't.

Turn signals & dead batteries:  The 993 being of European origin has a street parking “safety” feature where if the turn signal is active the marker lamp for that side of the car remains illuminated when the ignition key is removed. North American owners usually first encounter this feature when they go to start their 993 in the morning and the battery is dead, “It’s not a bug, it’s a feature!"

Battery Bummers: I read almost daily about cars with dead batteries. On the 993 the alternator, if running correctly, should produce enough current to run all the electrical accessories and still charge the battery. It may be helpful to get one of those eBay cigarette lighter plug voltmeters.

It should read a minimum of 12.6 volts or more for a good battery shortly after turning the engine off and from 13.5 to 14.2 volts or so with the engine running. A good test of battery capacity is to run your car and read the voltage at rest just a few moments after turning the ignition off then read the voltage after the battery has been sitting for four hours. If it has dropped below 12.4 volts and seems to try too hard to turn the engine over your electrical system has some sort of parasitic electric drain going on or the battery is a candidate for replacement. Overnight a good battery can drift down to 12.5 Volts +/- due to the normal parasitic loads in the system with the car parked, the turn signals off and the doors locked with the little light on the door flashing in single, not couplets, flashes every second or so. Also, I unplug the voltmeter from the constant-on stock lighter socket when I park my 993 even though it is unlikely to meaningfully contribute to the parasitic run-down rate of the battery. 

An alternative is to add a switched outlet to the dash, as I did, which provides a permanent home for a volt meter/USB outlet discussed on this page.

Here is a great page authored by Tore on Bergville FX  that discusses how to sort out a suspected parasitic loss problem.

All conventional car batteries sacrifice moisture from their cells as a product of the electrolysis process in the battery or simply evaporation. Even conventional so-called maintenance-free batteries have cells that need servicing and some can be pried opened and checked, others do not allow this but I am told can be MacGyvered and filled although it seems like a bit of an invasive process on YouTube. If you can check the fluid level in your battery occasionally and make sure it is full up to the fill indicator rings in the throat of each cell. Use distilled water for this purpose. For future reference, it may be advisable to look for a brand of battery that allows for topping off the cells next time your battery needs replacing.