I recently bought a 2004 911 from a used car dealer. When I went to pick up the car they were charging the battery. I was assured that the battery was new. The manager told me that he had owned multiple 996 models and he showed me the trick of leaving the trunk unlatched if I had periods when I wasn’t going to drive it. He told me that periods of non use would result in dead batteries and that this would make it easier to jump or charge. I went away for 6 weeks and as expected the battery was dead. Neither of my other cars had the problem. Is this really a problem that I should expect?

 

The dealer was likely not being truthful, but 6 weeks is a long time for the car to be inactive. Use a trickle charger when the car is not being used. There are many posts here about how to open a frunk (Front Trunk) when the battery is dead. There is a jump point in your fuse box. Also there is an emergency release cable hidden in the front bumper. Many people reroute the cable for easy access when needed. Leaving the frunk unlatched is likely to cause the light to be on, hastening the battery drain. Have the battery tested at a chain auto parts store. They usually will do it free of charge. (no pun intended).

 

Test battery voltage. You may have a parasitic draw draining the battery.

 

Thanks. I unplugged the trunk light before I went away for the 6 weeks to avoid battery drain. Guess the best is to trickle charge. It just seems odd that I can park my other cars for months while we travel but not the Porsche.

 

They do have parasitic draw, as do many modern cars, as computers, and security systems continue to run even when shut off.

A couple of things to consider, first, check your manual. There is a neat little feature on the fuse panel that allows you to jump the hatch opener if battery is dead (so no need to leave it open and disconnect light).

Second, apparently draw is less if the car is left locked.

Third, these cars can have a battery maintainer connected through the cigarette lighter plug, so no need to open hatch to actually access battery. This makes an easy connection for maintainer use when parked.

Last, I would agree with others, I'd have your battery tested. Three weeks to dead seems a little extreme. I've had mine go flat, but it was more like 6+ weeks. I now just connect my maintainer if I know the car will be parked for any extended period.

 

Dealer was charging the battery, so likely it was drained enough that the car would not start. New or not, car batteries do not last long once they have been drained, recharged, drained and so on. Car batteries are not deep cycle batteries and will last a long time with constant voltage. Thus the need for a trickle charger/maintainer. A brand new battery, car locked so all systems shut down, should last 6 weeks.

 

No need to unplug the light - the car's load management shuts the light off after 2 hours.

Load switch-off after two hours or five days
If the ignition key is removed, loads which are
switched on or in standby (e.g. power windows, luggage compartment lighting, interior light,
radio) are automatically switched off after approximately 2 hours.

 

You need a battery maintainer (aka float charger, aka battery tender) not a trickle charger for long periods of storage.
A maintainer keeps the battery topped up without overcharging; a trickle charger never stops charging, which can damage the battery.

You also want to close the frunk and lock the car.

 

I have a Battery Tender Junior plugged into the cigarette lighter (now 12v socket) but leave the car unlocked. Should it be locked as well?

 

Doesn't matter when on a tender.

 

+1

I’ll only add: if you do plan on doing any performance mods for your car, I would get the antigravity battery. It has a feature that all but eliminates a dead battery problem, and saves up to 25lbs or weight or more.

 

Agreed. Mine is unlocked all winter.

 

I have a trickle charger in the trunk sitting next to the battery (hidden) tied to the battery terminal with a short extension cord with the end routed next to the wiper and sitting in the area below the window and in front of the back edge of the trunk lid. you don't even see it. it is there all the time.

when I am going to be gone more than a week, I use an extension cord to the plug/wall outlet and drape the orange cord over the side mirror so I don't miss it when getting into the car.

That way you can lock the car.

 

You can also route the battery tender wire, when plugged into the cigarette lighter, through the notch in the door weather stripping, which is why the notch exists. The notch is located on the handle side of the door, up a few inches from the very bottom. The door can then close easily and be locked or not as you prefer.

 

Which door, driver or passenger? I didn’t know a notch existed!