Battery Trickle Charger pre-wiring install

**etyu** · 09-24-2007

For our friends that have long winters or those who store their vehicles, who wish to have a battery trickle charger while the vehicle "hibernates", this thread is for you.

I bought the Battery Tender Plus (r) Battery Charger this afternoon as I plan to trickle charge/condition the 12V car battery on weekends. I also decided to install the ring mount pre-wiring that came with the battery charger as I didn't want to deal with the battery clamps. This will make charging/conditioning the battery a simpler plug-and-come-back-later deal.

Below is a pix of the completed pre-wire install:

The red arrows point to the positive wire with the + ring terminal attached to the positive end of the battery.

The blue arrows point to the negative wire. This has been threaded through an unused rubber grommet (in the firewall to the battery compartment, highlighted by purple circle) and routed to one of the factory ground in the engine compartment (the bolt is highlighted by a round orange circle in the pix to the right). The negative wire is also anchored by plastic tie and covered with soft rubber at this junction (green circle).

The covered connector for the trickle charger is highlighted by the yellow circle to the left of the pix. This connector may be threaded out the vent at the front side of the battery cover if so desired. I probably will tuck this near the vent so that it is easy to locate and fish out with one hand. If not the battery cover is easy to remove anyways (just turn the three twist anchors 90 degress to release, one in front and two in the rear).

Tools needed: 10 mm hex head, a small 5-inch ratchet wrench (bought this for 98 cents at Marukai 98-cent store in Fountain Valley).

Tips and procedure:

1. Make sure to insulate the ratchet wrench while working to loosen the bolt at the positive terminal of the car battery. I used a small PVC tube that fits into the handle of the wrench. See pix below:

2. Thread the negative ring mount through the rubber grommet first.

3. The unused rubber grommet is easily removed by sliding upward (after the battery cover is removed). You will see a U-shaped cavity. Use a small chisel Exacto blade (2mm wide) to cut through the rubber that covers the u-shaped cavity. Follow the U shape so that the top of the U is uncut and the result is a U-shaped flap. The negative wire ring mount will go through the rubber grommet easily with minor effort and I used a rubber sleeve to protect this junction (purple circle). Cover the negative ring terminal with electrical tape temporarily to prevent short circuits.

4. Attach the positive ring mount to the positive end of the battery. I recommend wearing rubber/nitrile gloves when working at the positive terminal of the battery. Do not loosen the main ring that attaches to the + battery post or you'll loose your settings in the vehicle (e.g., electric seat memory settings, or preset radio stations). Loosen and remove only the 10 mm bolt and slide in the ring mount and retighten the bolt. I like the 7.5 amp fuse built into the positive wire of the pre-wiring for safety. Replace the flat red plastic that covers the positive battery terminal.

5. Route and anchor the negative wire in the engine compartment. Remove the electrical tape used earlier to cover the negative ring mount. Attach the negative ring terminal to the factory ground in the engine compartment (this uses a 10mm bolt as well).

6. Replace the battery cover. Or you may wish to start the trickle charge procedure. Follow the instructions as provided by the manufacturer. Do not plug into AC outlet until all the connections are done on the battery side of the trickle charger.

7. Happy trickle charging or conditioning the battery

I hope the above is helpful.

**Zeiser50** · 09-24-2007

I've done the same installation. Easy to use.

Is it a CTEK battery charger ?

**etyu** · 09-24-2007

The brand is Battery Tender. It works very similar to the CTek battery charger.

**DansSlk** · 09-24-2007

Nice one Eddy.

I have also done a similar rig except i made the harness myself and installed a waterproof connector with a cap on the end i then ran that down to the "gills" on the side of the bumper that does not house the oil cooler.

The connector is tiny and next to impossible to notice unless your really looking for it, when i want to hook up the charger i remove the cap from the connector and plug in the line from the charger that i modified so it has the option of the fittings i have installed on the SLK or the standard crocodile clips.

That then allows me to keep all the covers in place and everything locked up.

**DansSlk** · 09-24-2007

And again mate i am extremely impressed at the quality of your install right down to the rubber buffer to protect the wire at the pre-fuse holder tie you have.

**etyu** · 06-08-2008

I was thinking of routing a longer wire to the left front of the vehicle like DansSLK so trickle charging the battery can be done with the car bonnet/hood closed and/or the car doors locked.

Instead I mounted the trickle charger on the windshield (with rubber computer pad to prevent scratching the glass) and routed the wire differently. Didn't have to use extra wire after all. Piccies below.

The black battery cover (that protects the battery compartment from water/rain) should be removed first. This prevents the wire from being trapped between the rubber seal of the battery cover and the inner surface of the bonnet/hood when the hood is closed.

Photo below shows the battery cover removed and the yellow line shows how the wire is routed to the windshield area via a slot that allows water to drain from the front windscreen.

Trickle charger on windshield. Vehicle with engine bonnet/hood closed.

Edit: FOR INDOOR/GARAGE USE ONLY (protected structure)

Advantages:
1. No extra wire/cable needed.
2. Removal of battery cover, allows more ventilation especially with hood/bonnet closed during charging.

Disadvantages:
1. Battery cover has to be removed and then reattached after the charging process.
2. It doesn't look elegant nor as sohpisticated as DansSLK's set-up

mtiede · 06-08-2008

hmm.... If the wire to the battery is routed through the drain slot, won't water follow the wire from the drain right to the battery? That doesn't sound like a good thing.

**DansSlk** · 06-08-2008

I think Eddy park's his car indoor's so it wont be a problem for him.

Good work again Eddy!

mtiede · 06-08-2008

Just trying to provide a warning to Eddy or others who might be modeling after his technique in case the trickle might cause a trickle.

**Dave54** · 06-08-2008

I am not normally a do it your self kind of guy. But you folks are so helpful that I think this will be a project I will tackle. Thanks to all for the most helpful information

**etyu** · 06-08-2008

Quote:

Originally Posted by mtiede

hmm.... If the wire to the battery is routed through the drain slot, won't water follow the wire from the drain right to the battery? That doesn't sound like a good thing.

You're right mtiede. Thank you for pointing this out. (edit made to above post).

As DansSLK stated, the car is parked indoors.

The battery cover has a drain channel that actually routes water to the floor of the battery compartment, and drains out from there. There's also a drain right after the slot that drains water out before the battery compartment.

The battery trickle charger that I have is not for outdoor use either. It has vent slots at the top of the unit. Battery Tender does make one that is sealed and used to charge batteries in boats.

For those who park outdoors and wish to use a weather-proof battery trickle charger. DansSLK's set-up is the way to go.

ppower · 06-09-2008

Isn't there battery "tenders" you can get that just charge through the cigarette lighter?

Pp

**etyu** · 06-09-2008

Quote:

Originally Posted by ppower

Isn't there battery "tenders" you can get that just charge through the cigarette lighter?

Pp

Yes, BMW does that.

I tried using the same on MB vehicle, for it to work via cigarette lighter, key needs to be in position 1. ( I think it's because the cigarette lighter is switched). Same thing with 2003 Honda Odyssey.

**UK-C200** · 06-15-2008

etyu, your DIY skills are excellent. I think you have probably hit a great combination here - I'll be giving it a try!

ironchariot · 06-17-2008

Hi, and thanx for the detailed posting...could you please tell me, is there a challenge with connecting the negative ring lead from the quick connect to the negative terminal of the battery, or is there a specific reason for connecting the negative to a factory ground?
I connected both rings to their corresponding posts on my motorcycle for maintenance charging and haven't had an issue, and was wondering if I need to consider relocating that negative to a frame ground as well...
Again, thanx, posts like this give a lot of confidence to newbie DIY's!!!

**UK-C200** · 06-17-2008

Quote:

Originally Posted by ironchariot

Hi, and thanx for the detailed posting...could you please tell me, is there a challenge with connecting the negative ring lead from the quick connect to the negative terminal of the battery, or is there a specific reason for connecting the negative to a factory ground?
I connected both rings to their corresponding posts on my motorcycle for maintenance charging and haven't had an issue, and was wondering if I need to consider relocating that negative to a frame ground as well...
Again, thanx, posts like this give a lot of confidence to newbie DIY's!!!

Was doing some research on this very subject, and so far it seems that the advice stems from standard charging / jumping best practices, where using the frame ground reduces the chances of sparks and the associated explosion risk when making the connections with "clamps".

I talked to a mechanic friend of mine, and for "fixed" installation like what we are doing, he could not think of a really good reason not to use the terminal for the ground connection...

ironchariot · 06-17-2008

Quote:

Originally Posted by UK-C200

Was doing some research on this very subject, and so far it seems that the advice stems from standard charging / jumping best practices, where using the frame ground reduces the chances of sparks and the associated explosion risk when making the connections with "clamps".

I talked to a mechanic friend of mine, and for "fixed" installation like what we are doing, he could not think of a really good reason not to use the terminal for the ground connection...

Haha...I did the same thing with a mechanic friend of mine also, he thought it was fine to connect to the negative terminal as well...I just sent an email to Batterytender.com in hopes they will confirm for sure...I'll post here if they respond...thanks for responding UK-C200

!!!

09-24-2007	#1 (permalink)
etyu Founding Member #2 / Ambassador Of Good Will Join Date: Jun 2006 Location: Orange County, CA Vehicle: 2008 SLK 55 Posts: 4,912 Country: Thanks: 314 Thanked 207 Times in 107 Posts	Battery Trickle Charger pre-wiring install For our friends that have long winters or those who store their vehicles, who wish to have a battery trickle charger while the vehicle "hibernates", this thread is for you. I bought the Battery Tender Plus (r) Battery Charger this afternoon as I plan to trickle charge/condition the 12V car battery on weekends. I also decided to install the ring mount pre-wiring that came with the battery charger as I didn't want to deal with the battery clamps. This will make charging/conditioning the battery a simpler plug-and-come-back-later deal. Below is a pix of the completed pre-wire install: The red arrows point to the positive wire with the + ring terminal attached to the positive end of the battery. The blue arrows point to the negative wire. This has been threaded through an unused rubber grommet (in the firewall to the battery compartment, highlighted by purple circle) and routed to one of the factory ground in the engine compartment (the bolt is highlighted by a round orange circle in the pix to the right). The negative wire is also anchored by plastic tie and covered with soft rubber at this junction (green circle). The covered connector for the trickle charger is highlighted by the yellow circle to the left of the pix. This connector may be threaded out the vent at the front side of the battery cover if so desired. I probably will tuck this near the vent so that it is easy to locate and fish out with one hand. If not the battery cover is easy to remove anyways (just turn the three twist anchors 90 degress to release, one in front and two in the rear). Tools needed: 10 mm hex head, a small 5-inch ratchet wrench (bought this for 98 cents at Marukai 98-cent store in Fountain Valley). Tips and procedure: 1. Make sure to insulate the ratchet wrench while working to loosen the bolt at the positive terminal of the car battery. I used a small PVC tube that fits into the handle of the wrench. See pix below: 2. Thread the negative ring mount through the rubber grommet first. 3. The unused rubber grommet is easily removed by sliding upward (after the battery cover is removed). You will see a U-shaped cavity. Use a small chisel Exacto blade (2mm wide) to cut through the rubber that covers the u-shaped cavity. Follow the U shape so that the top of the U is uncut and the result is a U-shaped flap. The negative wire ring mount will go through the rubber grommet easily with minor effort and I used a rubber sleeve to protect this junction (purple circle). Cover the negative ring terminal with electrical tape temporarily to prevent short circuits. 4. Attach the positive ring mount to the positive end of the battery. I recommend wearing rubber/nitrile gloves when working at the positive terminal of the battery. Do not loosen the main ring that attaches to the + battery post or you'll loose your settings in the vehicle (e.g., electric seat memory settings, or preset radio stations). Loosen and remove only the 10 mm bolt and slide in the ring mount and retighten the bolt. I like the 7.5 amp fuse built into the positive wire of the pre-wiring for safety. Replace the flat red plastic that covers the positive battery terminal. 5. Route and anchor the negative wire in the engine compartment. Remove the electrical tape used earlier to cover the negative ring mount. Attach the negative ring terminal to the factory ground in the engine compartment (this uses a 10mm bolt as well). 6. Replace the battery cover. Or you may wish to start the trickle charge procedure. Follow the instructions as provided by the manufacturer. Do not plug into AC outlet until all the connections are done on the battery side of the trickle charger. 7. Happy trickle charging or conditioning the battery I hope the above is helpful. __________________ *Eddy* To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts. Pewter/Beige, PIII package, Airscarf, Hands-Free Communication System, Lighting package Designo Black Leather Cover on e-brake handle, ( To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts. Bill T), SmartTop v1.0, Kleyman 3BFM (NoRegret Custom), Green Air Filters, *Mod. R170 ant.* EuroClear sidemarkers w/PIAA PlasmaIon lamps, chromed front & rear turn indicator lamps, PIAA SuperPlasmaGTX front parking lamps, HyperWhite license plate lamps ( To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts. Scott), bilateral rear fog lamps enabled. Last edited by etyu; 09-24-2007 at 12:43 PM.
	http://www.slkworld.com/

09-24-2007	#2 (permalink)
Zeiser50 Elite SLK World Member Join Date: Mar 2007 Location: Paris Vehicle: SLK 55 AMG Other Toys: Bike : '84 Z1300-6 Posts: 494 Country: Thanks: 5 Thanked 8 Times in 8 Posts	I've done the same installation. Easy to use. Is it a CTEK battery charger ? __________________ To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts. ------Michel------ -SLK 55 AMG 2005-

09-24-2007	#3 (permalink)
etyu Founding Member #2 / Ambassador Of Good Will Join Date: Jun 2006 Location: Orange County, CA Vehicle: 2008 SLK 55 Posts: 4,912 Country: Thanks: 314 Thanked 207 Times in 107 Posts	The brand is Battery Tender. It works very similar to the CTek battery charger. __________________ *Eddy* To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts. Pewter/Beige, PIII package, Airscarf, Hands-Free Communication System, Lighting package Designo Black Leather Cover on e-brake handle, ( To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts. Bill T), SmartTop v1.0, Kleyman 3BFM (NoRegret Custom), Green Air Filters, *Mod. R170 ant.* EuroClear sidemarkers w/PIAA PlasmaIon lamps, chromed front & rear turn indicator lamps, PIAA SuperPlasmaGTX front parking lamps, HyperWhite license plate lamps ( To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts. Scott), bilateral rear fog lamps enabled. Last edited by etyu; 09-24-2007 at 04:07 PM.

09-24-2007	#4 (permalink)
DansSlk Super Moderator Join Date: Jun 2006 Location: Wales Vehicle: 05 B55S (Brabus 6.1 S) Posts: 6,458 Country: Thanks: 84 Thanked 137 Times in 107 Posts	Nice one Eddy. I have also done a similar rig except i made the harness myself and installed a waterproof connector with a cap on the end i then ran that down to the "gills" on the side of the bumper that does not house the oil cooler. The connector is tiny and next to impossible to notice unless your really looking for it, when i want to hook up the charger i remove the cap from the connector and plug in the line from the charger that i modified so it has the option of the fittings i have installed on the SLK or the standard crocodile clips. That then allows me to keep all the covers in place and everything locked up. __________________ One thing you will learn with German cars - If it's simple it ain't happening.

09-24-2007	#5 (permalink)
DansSlk Super Moderator Join Date: Jun 2006 Location: Wales Vehicle: 05 B55S (Brabus 6.1 S) Posts: 6,458 Country: Thanks: 84 Thanked 137 Times in 107 Posts	And again mate i am extremely impressed at the quality of your install right down to the rubber buffer to protect the wire at the pre-fuse holder tie you have. __________________ One thing you will learn with German cars - If it's simple it ain't happening.

06-08-2008	#6 (permalink)
etyu Founding Member #2 / Ambassador Of Good Will Join Date: Jun 2006 Location: Orange County, CA Vehicle: 2008 SLK 55 Posts: 4,912 Country: Thanks: 314 Thanked 207 Times in 107 Posts	Trickle charging with bonnet/hood closed I was thinking of routing a longer wire to the left front of the vehicle like DansSLK so trickle charging the battery can be done with the car bonnet/hood closed and/or the car doors locked. Instead I mounted the trickle charger on the windshield (with rubber computer pad to prevent scratching the glass) and routed the wire differently. Didn't have to use extra wire after all. Piccies below. The black battery cover (that protects the battery compartment from water/rain) should be removed first. This prevents the wire from being trapped between the rubber seal of the battery cover and the inner surface of the bonnet/hood when the hood is closed. Photo below shows the battery cover removed and the yellow line shows how the wire is routed to the windshield area via a slot that allows water to drain from the front windscreen. Trickle charger on windshield. Vehicle with engine bonnet/hood closed. Edit: FOR INDOOR/GARAGE USE ONLY (protected structure) Advantages: 1. No extra wire/cable needed. 2. Removal of battery cover, allows more ventilation especially with hood/bonnet closed during charging. Disadvantages: 1. Battery cover has to be removed and then reattached after the charging process. 2. It doesn't look elegant nor as sohpisticated as DansSLK's set-up __________________ *Eddy* To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts. Pewter/Beige, PIII package, Airscarf, Hands-Free Communication System, Lighting package Designo Black Leather Cover on e-brake handle, ( To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts. Bill T), SmartTop v1.0, Kleyman 3BFM (NoRegret Custom), Green Air Filters, *Mod. R170 ant.* EuroClear sidemarkers w/PIAA PlasmaIon lamps, chromed front & rear turn indicator lamps, PIAA SuperPlasmaGTX front parking lamps, HyperWhite license plate lamps ( To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts. Scott), bilateral rear fog lamps enabled. Last edited by etyu; 06-15-2008 at 07:26 PM.

06-08-2008	#7 (permalink)
mtiede Founding Member #7 Join Date: Jun 2006 Location: Western New York Vehicle: 2006 SLK 350 Posts: 1,381 Thanks: 60 Thanked 33 Times in 26 Posts	hmm.... If the wire to the battery is routed through the drain slot, won't water follow the wire from the drain right to the battery? That doesn't sound like a good thing.

06-08-2008	#8 (permalink)
DansSlk Super Moderator Join Date: Jun 2006 Location: Wales Vehicle: 05 B55S (Brabus 6.1 S) Posts: 6,458 Country: Thanks: 84 Thanked 137 Times in 107 Posts	I think Eddy park's his car indoor's so it wont be a problem for him. Good work again Eddy! __________________ One thing you will learn with German cars - If it's simple it ain't happening.

06-08-2008	#9 (permalink)
mtiede Founding Member #7 Join Date: Jun 2006 Location: Western New York Vehicle: 2006 SLK 350 Posts: 1,381 Thanks: 60 Thanked 33 Times in 26 Posts	Just trying to provide a warning to Eddy or others who might be modeling after his technique in case the trickle might cause a trickle.

06-08-2008	#10 (permalink)
Dave54 SLK World Member Join Date: Apr 2008 Location: Portland, Oregon Vehicle: 2009 SLK 350 Posts: 88 Country: Thanks: 47 Thanked 12 Times in 9 Posts	I am not normally a do it your self kind of guy. But you folks are so helpful that I think this will be a project I will tackle. Thanks to all for the most helpful information

06-09-2008	#12 (permalink)
ppower Senior SLK World Member Join Date: Feb 2007 Location: Central FL. Vehicle: 05' SLK55 Orion Blue Other Toys: CBR600rr, Mustang SC 480hp Posts: 113 Country: Thanks: 3 Thanked 4 Times in 1 Post	Isn't there battery "tenders" you can get that just charge through the cigarette lighter? Pp

06-15-2008	#14 (permalink)
UK-C200 Elite SLK World Member Join Date: May 2008 Location: London, UK & Baton Rouge, Louisiana Vehicle: 04 RHD C200K Coupe, 06 LHD SLK-350 Other Toys: Nacra F18 Posts: 314 Country: Thanks: 19 Thanked 66 Times in 35 Posts	etyu, your DIY skills are excellent. I think you have probably hit a great combination here - I'll be giving it a try!

06-17-2008	#15 (permalink)
ironchariot SLK World Member Join Date: Jun 2008 Posts: 12 Country: Thanks: 0 Thanked 2 Times in 2 Posts	Hi, and thanx for the detailed posting...could you please tell me, is there a challenge with connecting the negative ring lead from the quick connect to the negative terminal of the battery, or is there a specific reason for connecting the negative to a factory ground? I connected both rings to their corresponding posts on my motorcycle for maintenance charging and haven't had an issue, and was wondering if I need to consider relocating that negative to a frame ground as well... Again, thanx, posts like this give a lot of confidence to newbie DIY's!!!