chasles22

Hey!

I just bought my first Porsche, an '88 928S4 a few weeks ago. I've loving it! i am also learning very valuable German lessons nearly every time i touch it. recently i discovered (As i travel for work) that it misses me when i am gone for 2 weeks and wont start when i come home. The batt was fully flat. i have a high current battery conditioner and maintainer which brought the battery back to life, and to charge it i followed the 928 owner's manual's suggestion and removed the battery completely.

which leads me to my question: i want to use a very small battery maintainer (not my jumbo one, but a 1.5 or 2A model) and wire in leads etc. This may seem obvious but i want to know explicitly: is it ok/recommended/correct to attach the maintainer to the boost points under the hood? i read the whole battery charging FAQ and there's lots of opinion on frying the electronics/losing the injection memory etc etc and lots of recommendations to take the battery out to charge it etc as well as contrary opinions, but no where does anyone just say "yes hook up the battery maintainer to the boost points under the hood, that will be ok."

so, ya. long post for a simple question. can i put a trickle charger on this thing without having to pull the battery every time i am leaving for a few weeks?

dr bob

Simple answer to your question is... Yes. You can attach a maintainer to the jump post.

Now some more reasoning and experience to consider. M car sits for weeks at a time while I travel on business. My 'normal' parasitic drain is well south of 50 milliamps, so a couple weeks isn't a no-start. So I tried a maintainer, a Schumacher 1.5A automatic unit. It keeps the battery charged just fine, but... The constant cycling seriously shortens the life of the battery, as the maintainer cycles on and brings the voltage up, then shuts off and the parasitic load drains the voltage enough to cause the maintainer to cycle back on again.

In consideration of your two-weeks-to-dead parasitic load, you need to a) find the cause of the drain, and/or b) replace your toasted battery. Start with task a, and figure out where the power is going when parked. It's tough on the battery discharging it so much even if it's days between drives. After that, plan on lifting the ground strap at the rear rail under the tool cover when the car is parked for more than a week. Why beat up the battery and steal life from it unnecessarily?

With all that, I ran a charge pigtail with the ground strap down into the battery well. My battery is vented externally to the box with plastic tubing. So I can charge or maintain the battery with the ground strap lifted. When I park the car during extended sessions, I leave the hatch popped up out of the latch, so no problem with the maintainer cable running into the boot. The car sits covered so no problems with the cable in the way or being forgotten.

BSnyder

Dr Bob makes several good points. I run my maintainer throught the jump post in the engine bay, and haven't had any problems.

dr bob

Oh, and welcome to the group! Add your location to your profile (User CP at the top of the page) so we know where you are. Lots of support around the country and the world from members here. In the next couple months there are two major gatherings of owners. Frenzy is in a couple weeks on the east coast. Sharktoberfest is in Anaheim later in October.

Lots of information and support here. Invest in a Rennlist membership, and help support the pop-up-free environment. It's one of the better investments you'll make in your new car.

jcorenman

I'm using a couple of these CTEK 3300 charger/maintainers, they seem to work well:

Whitesands

I've been using the Harbor Freight automatic battery float charger for years.
Cen-Tech - Item#42292

The battery in the 928 is now over 5 years old which isn't bad considering that the 928 does seem to have an apatite for batteries.

chasles22

Excellent info thanks guys. I updated my profile, I'm in hamilton ontario. I bought this schumacher unit to use as the trickle charger:


which i read quite a few reviews of here... I've got quite a lot of projects on this car (mostly minor stuff like the battery drain) which i will accomplish this winter. For now, I need a simple solution whilst I'm gone. I AM really glad to know that if the electronics are touched up and the battery is good i dont need to worry about it, it gives me a good target.

now, about changing the brake fluid

my kingdom for a service manual....

WallyP

I like the Battery Tender Plus.
http://batterytender.com/battery-ten...-at-1-25a.html

While it is more expensive, since I had a Harbor Freight model fry a battery on long-term storage (not a 928 application), I am a little leery of the cheapies.

The Plus model comes with a long lead to the battery, and a polarized connector on the end. You get one end with ring terminals, and one with alligator clips.

This allows you to install the ring terminals to the jump start terminal and body ground, run the cord out to the grille and fasten it there. Set the tender unit up nearby, and fasten the long cord to the wall or workbench. The charging cord will only hook up one way, so your wife/SO/kid can't hook it up wrong. With this setup, if someone forgets to disconnect the tender, the cord simply pulls apart with no damage or risk.

This also leaves the other cord with alligator clips to use on other vehicles, the mower, motorcycle, extra battery, etc.

That being said, after I got the Plus, I spent several days finding and fixing the current drains on my 928, so I don't use it any more. As dr bob said, that is the best answer.

WallyP

If you want the "auto disconnect" feature for your Schumacher:
Buy a two-prong extension cord, choosing a length that will allow you to mount the maintainer in a convenient place. Make certain that the extension cord has a polarized plug and outlet, so the plug will only insert in one position. Try to find a cord that allows the plug to be inserted from the end, in-line with the cord, to ensure that it will uplug with a pull on the cord.

Cut the cord and install ring terminals on the cut end of the plug section. Install on the car, mounting the plug in a accessible spot in the grille. Splice the socket end to the maintainer, and mount the cord firmly to the wall or bench, leaving the socket so it reaches the plug in the grille.

You can also get another extension cord and a couple of battery clips so you can use the maintainer on other vehicles. Cut the socket off and put the clips on the end of the cord, being very careful to maintain polarity.

Fogey1

Morehouse manuals CD set. A cheap kingdom. Full of other info, too.
https://rennlist.com/forums/928-foru...n-cd-long.html

Well worth the price (Like a membership )

http://s287999742.e-shop.info/shop/a...ET-CD-Set.html

SanDiego928

Good question and great answers. Thanks.

chasles22

Thanks Fogey1!!!

i also found these here:
full service manuals for 928

Livio928

I am also in Hamilton. I have a MaxJax lift, the DT999 Diagnostic Tool if you have an 89 or newer 928, torque wrenches, some specialty 928 tools, and a bunch of hand tools. There are a few of us 928ers in the area who are quite knowledgeable and are more than willing to give a hand when needed.

I use a battery maintainer that I purchased from Great Northern Battery on Parkdale and it works(ed) great. Engine is out of car doing a complete rebuild.

chasles22

Livio, if you like beer it might be love at first site!! I could definitely use a little help and I have my own areas of expertise I am happy to lend too! I'll send you a PM...

westija

Taking the opportunity , but not kidnapping the thread....Does anyone have a number for maximum acceptable amperes drain , as a reference?
I might have the same issue but did not get to that just yet