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Discussion Starter · #1 ·
Documenting the install of a cable to access the 12 volt battery from outside the vehicle. There have been many posts about this project scattered around the forum. This will allow you to maintain the 12 volt battery and also give you an access point outside the frunk which WILL NOT OPEN if you have a dead battery.


Battery Tender cable. These are just long enough, have a decent weather cap for the connector, and are close to universal (aside from NOCO). Will be keeping a NOCO adapter in the car, as that's what we use. The Battery Tender works with Shumacher and a few others. If you go with a NOCO cable, you will need the large ring version.
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NOCO adapter.
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10mm socket for the chassis Ground. I tried to connect to the battery Negative terminal, but couldn't get the clamp bolt to completely back out. Like it was kept on with a retainer. Chassis ground is preferred anyway. Routed the cable through the vent in the upper plastic shroud.

Disconnect the Negative side before you begin this project.
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13mm wrench for the battery Positive. It will screw all the way off. The ring for the Battery Tender must be bent to clear the recess in the plastic battery cover. Swing the ring around to the back so the Positive terminal cover can snap back into place.
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Used a something similar to these to hold the connector in place.
I already had some on hand but the adhesive was old and wouldn't stick to the plastic, so I replaced it with some heavy 2-sided 3M automotive tape. Zip tied tightly. Wipe the area with rubbing alcohol to ensure adhesion.
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Access cover back in place.
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You can just see the connector peeking out below the wiper.
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$20-25 and maybe half hour of time to eliminate the major headache of replacing a completely dead 12 volt battery.

The problem is documented here and in a few other threads:
 

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FWIW, both positive and negative battery posts unscrewed completely for me, so that the ends of the cables could be bolted down securely around the bottom of the posts. Someone else screwed their cable ends to the battery posts using worm clamps, which isn't really necessary (and isn't as clean an installation).
 

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I got this one:


It comes with the cables to connect to the battery, like the instructions above. I like that the charger communicated with my smartphone via bluetooth so that I can see the status of the process. I had a different charger that gave no indication what it was doing when it was charging.
 

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Discussion Starter · #5 ·
I have mostly NOCO 2 amp and 5 amp units. A couple of older Battery Tenders hanging around too. The 5 amp has a "repair" mode which seems to have restored a bit of life to the few flooded cell batteries I still have. I've switched to AGM for almost everything.

One important thing to keep in mind is that the Battery Tender cable in the first post comes with a 7.5 amp blade fuse. Hooking up a big battery maintainer unit to it may put you back at square one should the fuse pop since it's sitting under the frunk.
 

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I got this one:


It comes with the cables to connect to the battery, like the instructions above. I like that the charger communicated with my smartphone via bluetooth so that I can see the status of the process. I had a different charger that gave no indication what it was doing when it was charging.

Do you know if there is a power interruption to the charger will it stay in the lithium ion charging mode?
 

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Stupid question . My RS is only coming end of the week , but regarding the 12v issue , isn't there like a 12v firelighter inside of the vehicle so you could use a CTEK to power the 12v ? in my Porsche i did it that way.
 

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TY for the write up, I plan to eventually do this once winter arrives.
ATM, if I am going away for more than 4-5 days, I just pop the frunk and leave a bright color towel wedged in the spring latch. Just in case...
 

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TY for the write up, I plan to eventually do this once winter arrives.
ATM, if I am going away for more than 4-5 days, I just pop the frunk and leave a bright color towel wedged in the spring latch. Just in case...
Curious why you would do this? I've had my car parked in the garage for 2 weeks and have no issue. I don't want to be fooled into going down a rabbit hole of doing a bunch of unnecessary things to my car lol
 

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Curious why you would do this? I've had my car parked in the garage for 2 weeks and have no issue. I don't want to be fooled into going down a rabbit hole of doing a bunch of unnecessary things to my car lol
Because if it does happen to you, you have zero options other than to have your car towed to the dealer. It happened once to me when my GT was on top of a hauler. Believe me it is not fun. It isn't a rabbit hole IMO. It took me 5 minutes to buy a charger, and another 5 minutes to hook up the wires. Now I have access to the battery without opening the frunk if that should ever happen again.
 

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Because if it does happen to you, you have zero options other than to have your car towed to the dealer. It happened once to me when my GT was on top of a hauler. Believe me it is not fun. It isn't a rabbit hole IMO. It took me 5 minutes to buy a charger, and another 5 minutes to hook up the wires. Now I have access to the battery without opening the frunk if that should ever happen again.
And based on other forum reports, just getting vehicle towed is another story in itself. Tow dollies, physical pulling of straps tied to the wheels, etc..
 

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Because if it does happen to you, you have zero options other than to have your car towed to the dealer. It happened once to me when my GT was on top of a hauler. Believe me it is not fun. It isn't a rabbit hole IMO. It took me 5 minutes to buy a charger, and another 5 minutes to hook up the wires. Now I have access to the battery without opening the frunk if that should ever happen again.
Good enough...learn from others experiences! Thanks for sharing. Will the exposed cable become faulty over time though from weather sticking out from under the hood? Is there a cap avail for it?
 

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Because if it does happen to you, you have zero options other than to have your car towed to the dealer. It happened once to me when my GT was on top of a hauler. Believe me it is not fun. It isn't a rabbit hole IMO. It took me 5 minutes to buy a charger, and another 5 minutes to hook up the wires. Now I have access to the battery without opening the frunk if that should ever happen again.
There's a 12V lead in the driver's side footwell fuse panel for opening the frunk in the event of battery power being lost. You're not completely locked out of the frunk without a permanent charger connection.
 

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I'm curious if anyone has tried just running the positive lead from battery and waterproof it
There's a 12V lead in the driver's side footwell fuse panel for opening the frunk in the event of battery power being lost. You're not completely locked out of the frunk without a permanent charger connection.
The fuse panel/door jam option doesn't appear to be applicable for US market.
TSB
 

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I'm curious if anyone has tried just running the positive lead from battery and waterproof it


The fuse panel/door jam option doesn't appear to be applicable for US market.
TSB
The lead is there, so I'd be surprised if it's not wired up. I was just hardwiring my dashcam this weekend and it's clearly there. Looks very similar to how it's worked on Porsches I've had in the past.
 

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Had some free time so decided to swing by auto store and grab battery tender cable. Made a minor change on mounting. A bit paranoid of heavy rains or car washing filling up the plastic shroud so I used 3M Dual Lock (used for front license plates) mounted to hood. Depending on how long your tender cable is, it may stay or detached upon frunk opening (I don't use the frunk).
Also measured voltage with Fluke multimeter and it looks good at 13.43V

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Discussion Starter · #18 ·
...
Also measured voltage with Fluke multimeter and it looks good at 13.43V
Checking the voltage on a somewhat-routine basis could alleviate concerns expressed earlier in the thread about the connector failing or being too weathered over time.

After my install, I measured 13.58 volts.

Tucking it up under the hook is a good idea.
 

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Discussion Starter · #20 ·
Wanted to post my experience with an exposed battery maintainer cable.
This one has been on my tractor for at least five years. Probably more like 7 or 8. The machine lives under a shed roof but is otherwise exposed to elements.

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Zero corrosion. Full voltage from battery.

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There will be no issues with a cable under the hood on the GT.
 
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