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Disconnect, rather than Maintain, Battery?


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Over the holidays, my 2001 Boxster 2.7 sat idle without a battery maintainer. I jumped it, drove it out on the interestate and it worked well. It had about a week between that time and the next successful start. It's been just over a week since I last started it-- about 10 days-- and it is now dead again. I should mention that the car has a new Interstate battery as of May 2004. It was in the car when I bought it in September. I have had no problems starting the car until I basically stopped driving it once a week.

I've scoured the archives and found that there is a steady draw on the battery from various electronic equipment in the car (alarm system, remote access, etc.) but I just want to be able to disconnect the battery, leave the trunk ajar, and connect it when I want to use it like I did my 1981 Porsche 928.

I sense that this car will have a fit if I do that. One, it has an electronic odometer. Two, I'm guessing it has EPROMs that will zero out and require it to "learn" how to drive after I start it again. Three, it has the remote start.

If I leave it unlocked, leave the front boot ajar, what would be the downside to just disconnecting the negative lead rather than messing with the maintainer (which also has a hydrogen gas issue, however minor, in an enclosed garage)?

I did this successfully for years with my 928.

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Moose, I prefer the "Battery Tender".. and have three I rotate among my three bikes and two cars, which I have done for long enough to know it saves battery $$$, but that is not the main concern. When out of service this way, whether you disconnect it or remove it you want to charge it with a charger before you put it in service, NOT the vehicles alternator...which is designed only to issue a maintenance or "surface" charge. In many years of selling these parts it is my belief that this type of use causes premature failure of the charging system components more often than any other cause.

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Blakbox,

I appreciate the response. Using a battery maintainer is not an option for me at this time.

Do you think that disconnecting the battery will have an adverse effect on the odometer and other electronic equipment. Rereading my own post, I think I answered my own question. My guess is that the equipment that 'stores' digital information is in fact an EPROM that doesn't require an outside source of electricity.

However, I have read that when people hook up their batteries after some time, wierd things happen to their odo's and on other cars, I've heard about coughing and sputtering due to the fuel injection management software needing to relearn how to drive.

Edited by Moose
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I've heard about coughing and sputtering due to the fuel injection management software needing to relearn how to drive.

It won't be that bad. The idle will hunt for a few minutes and torque/rev range will also adjust fairly quickly. The car will certainly be drivable but don't expect top performance for a few miles.
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What about a solar charger?

You mean, to charge the sun?? Doesn't that bad boy stay charged on it's own?

Sorry, just goofing.

Wingless - I see you are from RI - whereabouts? (probably better to reply in email so as not to corrupt the thread). I lived there for my first 30 years. In fact, I bought my MY98 from someone in New Hampshire while visiting my parents in Chepachet. Sorry for threadjacking. We now rejoin our original topic, already in progress.

I've been wondering about trickle chargers for a while. Apparently a lot of folks here have them - do they monitor the charge of the battery to avoid overcharging?

- Pete

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When out of service this way, whether you disconnect it or remove it you want to charge it with a charger before you put it in service, NOT the vehicles alternator...which is designed only to issue a maintenance or "surface" charge.

I do not agree with this statement. There is no way that an automobile's alternator is designed to only issue a maintenance or "surface" charge. It is designed (amongst other things) to recharge the battery after starting the car. That is charging the battery not a maintenance or surface charge. The alternator can put out in the neighborhood of 50 amps. It will fully recharge the battery, depending on level of discharge, in 15-30 minutes.

If the car is out of service for a week or so with the battery disconnected, assuming the battery is in good shape, it is not necessary to charge it with an external charger. Even several months should not be a problem. If a disconnected battery does not hold a charge on its own for several months there is something wrong with it.

Re: trickle/float chargers

Theoretically these are different. A trickle charger is a slow charger. A charger that takes 8+ hours to recharge the battery. Your typical 5-10 amp automobile battery charger is a trickle charger. It usually keeps charging as long as it is connected.

A float charger is usualy used to maintain a battery. It monitors the battery voltage and modifies its charge rate as appropriate. Most automobile float chargers operate in the .5 to 1 amp range while charging dropping to zero when not needed.

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A float charger is usualy used to maintain a battery.  It monitors the battery voltage and modifies its charge rate as appropriate.  Most automobile float chargers operate in the .5 to 1 amp range while charging dropping to zero when not needed.

Thanks for the lucid reply.

I have a trickle charger that I seldom use; I guess I was reading these posts and confusing a float charger with a trickle charger.

Thanks again.

- Pete

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The alternator can put out in the neighborhood of 50 amps.  It will fully recharge the battery, depending on level of discharge, in 15-30 minutes.

Try ~110 amps for 986 alternators. The cayenne is 210 amps max output! Still, this is a moot point because if the alternator needs to fully charge the battery, the battery is probably bad and will lose the charge from the alternator as soon as the car stops running anyways.

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The alternator can put out in the neighborhood of 50 amps.  It will fully recharge the battery, depending on level of discharge, in 15-30 minutes.

Try ~110 amps for 986 alternators. The cayenne is 210 amps max output! Still, this is a moot point because if the alternator needs to fully charge the battery, the battery is probably bad and will lose the charge from the alternator as soon as the car stops running anyways.

Regardless of the output of the alternator, it will always try to fully charge the battery. As soon as you start the car the alternator will be charging the battery to replace what was used to start the car. Whether or not the battery will hold the charge is another matter.

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