Battery Cut-Off Switch

Richard-Dublin · 02-21-2005, 05:32 AM

My nearly new battery tends to go flat if my '89 3.2 is left for a couple of weeks - this seems to be a fairly common problem with 911s. It doesn't really bother me because I have now started to use the battery cut-off switch after I drive the car. However I'm a little worried that reguarly disconnecting the battery may harm some of the car electronics - do I need to be concerned?

Paul Franssen · Paul Franssen's Garage

Why don't you put an inexpensive trickle-charger onto your battery? My '88 has the same problem (battery emptying) but with the trickle-charger (the kind that checks the charge status and acts in consequence, so it doesn't overcharge), the battery is always 100% ready for use, and the alarm works...

NY65912 · 02-21-2005, 06:27 AM

Ditto on the trickle!

ADRNLN · ADRNLN's Garage

When I bought my car, the previous owner had a cut-off knob at the battery terminal, which posed a hair-pulling problem. The car would occasionally not start, but after waiting a minute, it would start up. After chasing down all sorts of potential problems, it turned out to be the damn battery kill knob. It was ever-so-slightly loose which caused a weak continuity connection.

Apparently, one crank of the ignition sent enough of a jolt through the system to cause the metal to expand just enough to make contact, enabling a second crank attempt to work. Such symptoms brought to mind all sorts of potential causes, from faulty ignition switch to erratic starter motor solenoid to other electrical or fuel problems.

It was a pesky little problem, but turned out to be a simple answer.

--Steve

Richard-Dublin · 02-21-2005, 12:48 PM

Unfortunately my garage has no power (and is away from the house) so a trickle charger isn't really an option at the moment - do you think turning off the battery is doing any harm?

t.brady · 02-21-2005, 12:54 PM

richard, check out this thread. sherwood has a good idea and i believe it's relative to your point.

galwaytt · 02-21-2005, 01:04 PM

Richard - hello from Galway.
If, like me, your car spends more time parked rather than running, then you need to disable the alarm too. That'll kill the battery inside 2 weeks, and if your garage is cold, that'll speed up the process - I see it's knowing there today.

You can get the good Odyssey batteries from Tim Molloy in Dublin - I just got two for the bikes this week, because the BMW bikes are notoriously fickle on the battery front too..............

I can get you his no tomorrow, if you want.

P.S. you need to move the garage-electricification project up the list !! How far away is it? It'd be cheaper than renewing 911 batteries................

P.P.S. are you in the Porsche Club here? Trackday at Mondello in March - I'm bringing my 87 3.2

mike f · 02-21-2005, 03:12 PM

When you use a battery tender, do you leave the trunk lid open? I would assume so, but wouldn't the trunk light always be on then?

NY65912 · 02-21-2005, 03:23 PM

The mercury switch for the trunk light shuts the light about 6" from closure. I got down and watched the light go off. But to be honest, I disconnected it also. I have a heavey duty extensin cord into the trunk and plugged into the tender....snaked under the car cover.

strupgolf · 02-21-2005, 04:16 PM

I also use a cut off knob, and so far I love it, after doing much work on the electrics over the last few months. My question is this. I have a Shuemaker brand trickle charger. It has a yellow[charging], green[charged], and red[problem] set of lights. When I hook it up, it lites up yellow, and after 5-10 minutes, it goes red, to problem. What am I doing wrong? I just want to keep it charged up. Thanks

Wil Ferch · 02-21-2005, 04:29 PM

Mercury switch?.....for the trunk light?

Isn't it a simple "plunger" switch?

PS---do a search on stand-by power draw/leak...it might also be a bad dome light door switch that keeps the power wondow relay ( incorrectly) energized at "all" times. Should be de-energized after it allows a "one-time" closure of windows after engine is shut down....

Wil