Hardwiring battery maintainer proposal

Thinking about hardwiring a battery maintainer connection to the exterior of the vehicle. This would allow me to plug the battery tender via an accessible connection on the exterior vehicle so that I could park with the doors/windows closed and still maintain a connection to charge the battery . Haven' figured out where to hide it, but probably somewhere in front grill. The idea is to have the connection inactive when the battery tender is not attached (so that you can't short it), but when the battery tender is attached, coupling the connector leads to the battery . I was thinking of using a standard Bosch relay with the following connections: 85 = + terminal of battery maintainer 86 = - terminal of battery maintainer (and also to Battery (-) 30 = coupled to battery (+) via 5 amp fuse 87A = + terminal of battery maintainer 87 = N/A The Bosch relay would keep the connector normally open (common ground would remain attached) when the charger unit is not plugged to the connector, but when the charger is attached, the relay would close the switch to couple the + battery terminal to the + connector end, allowing charging of the battery. Since the Bosch relay only draws about .2 amps, it shouldn't impact the charging unit too much. The only tricky part is that the battery tender has an auto shut off feature once the high end of the battery charge has been reached, which may cause the relay to possibly activate and deactivate periodically or continually. Not sure if the relay can handle this. Does this seem like a viable solution or is there more preferred circuit arrangement? Here is picture of the battery tender junior with the plug connections

Why Make Things Difficult? Buy the CTEK 3600 Battery Maintainer (Same as the Porsche one - But Cheaper because it does not have a Porsche Sticker) CTEK MULTI XS 3600 - Features It has 2 Ring Connectors to Permanently Attach to your Battery Terminals....... I lead the cable out of the Front of the Battery Cover, and Out under the Hood and Hold it with the Wiper Blade - Connect when Necessary and Hide under the battery Cover When Driving.......................

If you use a tender with a socket plug (and you can modify the tender to have the plug ) there is plenty of room for the battery tender wire to exit around the front door without having to worry about leaving the window down or the door open. See the photo in my gallery with examples of two sizes of electric cords as examples. No need to get this complicated.

I agree with Karel - why not just attach the extra charging cable (the one with the ring connector leads in your picture) and run the end to someplace convenient to plug -in. You might have to fabricate an extension cable to get it to reach the front grill, but you probable could just zip tie it up there somewhere convenient.

This is exactly what I do. There is a socket plug available for the Battery Tender , even an extension cable, and I plug into the console lighter and route the cabling through the bottom of one of the doors. Laid flat, the cable will compress the weatherstripping a bit, but otherwise there's no problem. BTW, the Ctek is over-priced, compared to the equally capable Battery Tender . A Battery Tender Junior works just fine, so long as you're not expecting a quick charge. I also think the Junior is actually safer, because it only puts out 750 milliamps.

I'm with the other guys. Use the cig lighter. If you really want that external connection, your relay application will not work. As you described it, the relay will open the second you apply the maintainer and break the connection to the battery . Not to mention, you would not accomplish what you hoped because the connector could be shorted and the fuse blown from the outside because you are passing current through the normally closed side of the relay contact. If you tried to reverse the 87a and 87 contacts, you could theoretically accomplish your goal, but the first time you use the maintainer it will activate the relay and close the circuit. Current will then back feed from the battery to the relay keeping the relay active (and drawing 100ma) after you remove the maintainer. This will kill your battery and ultimately the relay too. You could diode isolate the circuit to prevent that, but it you're going to do that, you might as well just use a 6 amp diode on the + line going to the maintainer. A diode allows current to flow in only one direction, to the battery , not out of the battery . The drawback to this method is that most 6 amp silicone diodes will displace 0.6-0.9 volts of positive bias voltage, ultimately reducing your charging voltage by that much. That may not be a real problem, but I am not sure how your battery maintainer would like that. If it reads voltage to determine when to apply a charge, it's not going to see any because the diode won't allow the battery to flow current to the maintainer. The easy fix, do what the others have suggested.

I think you guys have me convinced to just route under the door and use the cig lighter. Alhough it's strangely reminiscent of how I charge my daughter's barbie jeep

LOL! :hilarious:

My battery tender plus came with cable set that attaches to the battery terminals. It has a cap on the other end. My charger is in the front of the garage. When I use it, I just pop the hood and hook it up. Then I lower the hood, without it latching and all is well. Each and every time I get to remove and install the black plastic battery compartment cover. It provides me with the opportunity to appreciate the effort that went into the design and creation of this cover. It's a work of art

Some call it the work of the devil then they try to replace it....

Would have to support the CTEK idea -- have had one installed for several months & it works great when needed. Also, fyi, the pigtail/ plug comes with a cover that prevents water & shorts.

If you hook a pig tail to the battery add a 5 amp in line fuse within 6-8" of the battery post. In fact any aftermarket wires to the battery need a fuse @ the battery post.

That is a good idea. Haven't purchased a maintainer, as I can't see myself always routing it inside. A more permanent and quick way appealed, but didn't like the idea of a possible short causing a red hot wire. Ease of plug in/out is what seems to be the want.

Complete support for the simple approach. There is a structural beam in my garage which runs the same axis as front to back of the Cayman. It is also directly over the steering wheel. So, I mounted a surge protector on the beam and hung a cup hook. I have the excess wire from the tender "twist-tied" close to the cigarette lighter socket end. I hang those coils of cord on the cup hook when I'm driving, and then when I return, I reach up, grab it, and reinsert in the lighter socket. The tender goes on a shelf in the summer, but it could stay hung year round. Takes 5 seconds to store when I'm going driving, and 5 seconds to plug in when I return. Total cost under $20 and no electrical engineering degree required. Plus, no battery worries!