Battery tender/maintainer question

ChemMan · ChemMan's Garage

I wanted to make sure I was doing this correctly before setting it up. I have a DieHard battery charger/maintainer Model no. 200.71220. I want to leave the battery hooked up in the 911. There are a couple of items to take care of this winter that will require the battery be installed. So, I assume that I cannot simply hook the tender right to the battery. Is it correct to connect the positive terminal to the positive clamp of the tender and the negative to the chassis?

Thanks in advance....only a few months till driving season

nineball · 12-12-2009, 05:18 AM

you can leave the battery in the car and just hook the tender directly to it. it will charge until full, then it will turn off and monitor the battery. if/when it falls below 13.2v the charger will kick on again until it is full, then repeat the cycle.

motorcop · 12-12-2009, 05:45 AM

I leave my tenders hooked directly to the battery with the cables attached as normal. Same on my motorcycle, set it and forget it, you won't have any problems.

Paul Crowther · 12-12-2009, 06:24 AM

me 3.
Paul

TCallas · 12-12-2009, 06:39 AM

Chem man, I cannot speak for safety of your "Die Hard battery charger/maintainer Model no. 200.71220" and this will be the determining factor. It is fine to connect a battery maintainer directly to your battery and even through the cigarette lighter via a cigarette lighter adaptor. If this is for your 1986 911 it's a fairly simple process to access the battery ground terminal but not the positive terminal. Be careful, the battery ground terminal should be the forward (direction of the car) one. The positive terminal, due to its location makes it easy to short out on the chassis. I personally use the Battery Tender and Porsche brand battery maintainers.

nineball · 12-12-2009, 08:03 AM

the diehard one is basically the same thing. it charges at 1.5v until it reaches 14.4 and then drops down to half a volt while in "float" mode. at 13.2v it kicks back on at 1.5v.

911pcars · 12-12-2009, 09:28 AM

TCallas is correct in the difficulty of connecting the charger connector directly onto the positive battery post/terminal. A workaround is the aforementioned use of a cig. lighter adapter, but this only works if this circuit remains hot (ON) when the ign. is OFF.

Another strategy is to connect the maintainer directly to one of the constantly hot fuse circuits in the fuse box (snip off the clamp); maybe easier accomplished on early 911s than later models with less accessibility to the wire connection under the fuse block.

With the maintainer semi-permanently situated in the trunk, it's just a matter of plugging it into a wall outlet when the car sits.

Sherwood
SeineSystems.com
911pcars

ChemMan · ChemMan's Garage

Thanks for the info. All done, oil change, moth balls etc. Tucked in for the winter.

regency · regency's Garage

i have a 73 911 T Coupe with duel batteries. I had custom made negative cables made (2) and ran them from the negative posts to a hidden marine switch for security & ease of working on the car.

Now, I wonder the best may to apply my Battery Tender?

73 Aubergine 911 MFI T coupe, built to E spec
73 914 2.0 ( sold ) sad day
74 Alfa GTV ( currently in pieces - rust repair under way )

avale · 12-13-2009, 01:55 PM

FYI, my '87 has the cig. lighter plug dead when the ignition is off, so the cig. lighter charger doesn't work. I assume most Porsches are wired the same way so try to heat up the cig. plug before you spend the money on the adapter.

Formerly Steve Wilkinson · 12-13-2009, 02:24 PM

Am I missing something? My battery tender came with a two-foot lead terminating at the battery end in eyelets that get hard-wired to the battery posts, and at the other end it terminating in a plug that mates with the long lead that goes to the Battery Tender. Park, plug, done.

avale · 12-13-2009, 02:33 PM

Quote:

Originally Posted by Formerly Steve Wilkinson

Am I missing something? My battery tender came with a two-foot lead terminating at the battery end in eyelets that get hard-wired to the battery posts, and at the other end it terminating in a plug that mates with the long lead that goes to the Battery Tender. Park, plug, done.

"Technically" you are suppose to ground to the chassis instead of the battery. Either will work...

Formerly Steve Wilkinson · 12-13-2009, 02:37 PM

That seems "technically" dumb. If you're charging a battery, you're charging a battery, not a car/battery unit. Yes, I know, there are a few thousand nannies out there who will tell me I'm creating a 21st century Hindenburg, but I'll go with the Battery Tender instructions.

avale · 12-13-2009, 03:15 PM

The Battery Tender instructions also say to ground to the chassis. http://www.batterytender.com/includes/languages/english/resources/Product_Instructions_BT_Junior.pdf

Formerly Steve Wilkinson · 12-13-2009, 04:08 PM

You're right, I must admit. But it is Lawyertalk. Once I have successfully hard-wired my plug to the battery (with my master switch off, thus isolating the battery anyway), I am safe forever from the Hindenburg Syndrome.

Dantilla · 12-13-2009, 04:13 PM

When the ground is attached directly to the chassis, what is the difference between attaching the maintainer to the battery's ground vs. attaching it to the chassis?

Formerly Steve Wilkinson · 12-13-2009, 04:26 PM

I _think_ the fear is that if you attach anything to the battery poles directly in the wrong sequence, you can create a spark that can ignite hydrogen being discharged by the battery. Of course hardwiring anything to the battery once and for all and then connecting a plug to the hardwired lead negates this danger.

But lawyers need to cover every arse out there, so if there's a possibility that the sky will fall upon you and Chicken Little, they will demand that you only hook up the Battery Tender while inside a bomb shelter, thus creating a society of ever-increasing Chicken Littles.

911pcars · 12-13-2009, 05:45 PM

Quote:

Originally Posted by Dantilla

When the ground is attached directly to the chassis, what is the difference between attaching the maintainer to the battery's ground vs. attaching it to the chassis?

As long as the connection is tightly secured to a clean surface, there is no difference.

"...if you attach anything to the battery poles directly in the wrong sequence, you can create a spark that can ignite hydrogen...."

Always disconnect the ground battery cable when connecting components to the system. Doing this minimizes any spark hazard. The battery produces the most hydrogen gas during charging.

Sherwood