Gary Knox

Harbor Freight sells a battery maintainer that I've been using on a variety of 12 V batteries for 5-6 years. I have a half dozen of these, frequently on sale for ~$10!!! These have worked great, and have not had a battery fail - in or out of a car during their usage. On the 928, I just clip it on the jump post and a ground. Other vehicles/uninstalled batteries I connect to the battery posts.

Gary Knox

JPTL

+1 on the reliability & value of the HF maintainers.

IrishLegend

I just got one of these and am wondering if the red light is supposed to stay on before and after pluging in to the outlet? I have it hooked up under the hood, not directly to the battery. Is this okay?

Thanks.

cold_beer839

I would recommend connecting it directly to the battery. Going from the hot post under the hood may not be good on your cpu.

I connected mine directly to the battery terminals and put the quick connect pigtail out the battery cable port in the battery well. It hangs down about 5 inches from the port opening, but can't be seen from behind the car, and is very easy to connect (after the tail pipes cool down!!).

inactiveuser1

Brian,
They said some 928's are wired different some trickle chargers may work plugged into the cigarette lighter some may not unless the key is on.
I know I tried it and would have to leave the key in the on position for it to work.Who wants to store their car with keys in it and in the on position with other accesories on?
So went and bought a unit at Auto Zone that would work with the cigarette lighter hookup and hooked direct to the battery.
This way its not going thru the whole wiring system either.
Took the ground strap off located behind the tool kit and mounted the unit right with the stock ground strap.When in use just undue the tool kit and plug the trickle charger in.Stored for long periods of time it keeps the battery up which will help with battery life.
Its a quick install and nice to hide when not in use.
Mounted in behind tool kit on angle allows to put the tool kit in place when not in use.
Hot wire goes to positive side of battery used with inline fuse.
The body of the unit mounts right with the ground strap which provides a very good ground.
This plug in unit I used with the same type of charger you are talking of right from the Porsche dealer that
has the cigarette lighter style plug.

JPTL

With the Harbor Freight maintainers, I believe that the red light indicates that it's sensing power on the battery end. I can only imagine that it's to ensure that you've got a closed circuit to the battery. So to answer your question, you should get the red light when the maintainer is properly connected to pos & neg; whether plugged in to wall current or not.
Re: where best to hook this up, I agree with Dave that hooking it up directly to the battery is a better setup than to the jump post. You're much further from the ultra-sensitive & pricey computer when connected to the battery. Also, the maintainer is getting a truer reading of the state of the battery. Why risk harming the brain?

You want to make connecting to the maintainer as convenient as possible. I used the original alligator clips and connected to the battery & ground strap. The module w/the red light fits next to the latch mechanism. A mini male/female audio connector spliced into the wire between the ac plug and the module with the red light works well, and provides a quick-connect pigtail as Dave describes. If you need longer wire, just make sure that you're using the same or heavier gauge wire than that of the maintainer. Of course your connections to battery positive and the ground strap should be nice & clean and secure.
Mine tucks up out of sight at the base of the tool cover when not in use. When plugged in, the hatch easily closes over the wire & I have a visible tag to remind me to unplug it before pulling out of the garage:

jpitman2

Direct connect to battery poles (fused 5A), so you can disconnect car at earth strap, but keep battery topped off. My socket is under license plate.
jp 83 Euro S AT 52k

IrishLegend

Thanks.

pcar928fan

My wire comes out of one of the holes in the bottom of the battery box and has a 10A fuse at the + post in case of wire chaffing and causing a short. I think tuck the "tail" that plugs in to the battery tender under the rear bumper cover... out of site and easy to access. No doors or hatches ever need be open to use the system. Works GREAT! Use it on Blue82 and on Euro92! AWESOME!

WallyP

There appears to be a great deal of unnecessary angst about using the jump start terminal under the hood. The jump start terminal is connected directly to the battery positive post thru fairly heavy wires and cables. Electrically speaking, there should be no difference in hooking to the jump start terminal and the battery. If there is a difference, you have some problems that need to be fixed...

The dangers in using the jump start terminal are the same as those in hooking directly to the battery - you should not use a high-power, high-voltage "booster" to start the car or charge the battery, and you should be very careful to avoid hooking anything up with reversed polarity.

mdkelly1

+1 on what Wallly said. Been using a "maintainer" on the jump post for a decade and it seems to work fine, even during very long storage periods. Good idea to check things occasionally though

pcar928fan

I don't like using the jump post because you either have to open the hood, or have wires passing to close to moving belts and pulleys and those would need careful securing to keep them out of the moving bits. I go through the battery box because it is easier for me all the way around... If I need to put my big charger on one of the cars that does not have the maintainer then I always go through the under hood jump posts...

jayc67

Just a single data point I will add, and it's just one occurrence so there may be nothing to it but.....

Over the summer I connected a battery maintainer to the under hood posts without verifying the charger was off (my fault no question) and I saw a single spark. My stomach turned because I just knew......

I saw cash fly out the window since I had to replace the LH brain with a rebuilt one from JDS.

I too have used that post for all the years I owned this car, with no problems until that one.

Never again will I use the under hood connector for any purpose.

Alan

So what...? Sparks mean nothing specific wrt voltage.. - you can get some good sparks when re-connecting the battery - it doesn't mean anything bad happened...

It was silly to connect the device when it was powered - mainly because you could possibly damage the charger by shorting it as you connect it... its also possible its regulation is worse when it sees a sudden change in load...

Connecting to the jump post is the same thing as connecting to the battery direct - as Wally noted there is a big solid wire back to the battery so there is no electrical benefit to a direct battery connection...

Any problems anyone ever had with a jump post connection means you had a connection problem on one of the connectors...most probably the ground.

Alan

jayc67

Well it does in this case since the car was running 10 minutes before I attached the maintainer, and the LH was dead from that moment on. Maybe the stars aligned and it was time, I don't honestly care. The damage was done.

Stupid to connect with the charger on? Of course it was.

The big difference is that with a direct battery connection I now have it wired in permanently rather than having to worry about making temporary connections which always have added risk it seems, or at least more opportunities to do something stupid. The price of a mistake is pretty high on this car.

I'll leave the engineering discussion to you and Wally and others, but for me I'll never use the post again. There is enough voodoo in the 928 electrical system for me to make irrational decisions about this.