Zamp vs Battery Tender

The battery tender is basically a trickle charger and when you park your trailer at home or wherever you store it this is a good way to keep your battery healthy, as it will maintain/float the battery charge when the trailer is sitting idle.  The battery tender does the same thing as your electric converter on your trailer, but obviously it takes a little longer for the tender to charge things up as it's a smaller unit and will take a few days to get the battery up to a full charge if it's been severely depleted.  

If you do use the battery tender remember to check the Zamp solar port connections and flip them as the polarity is reversed on the Zamp solar connector on your battery box and your battery tender will not charge the battery up.  You'd be better off to use the clamps that come with the battery tender and eliminate having to mess with the Zamp solar connections.


I use a permanently mounted 50 watt Renogy solar panel (with solar charge controller) on the side of my garage to keep the trailer battery charged up.  I also installed a battery switch so that I could eliminate (unhook the battery from the trailer) any parasitic drain (e.g. LED circuits, TV, etc. draining battery when sitting idle) when my trailer is sitting in my garage.  This works great and my battery is fully charged, maintained and ready to go when I roll out the trailer for my trips.  

Lisa33 said:

Do we know why the Zamp polarity is reversed?  Since the Renogy panels and the Battery Tender are both the opposite of the Zamp quick connect, Zamp seems to be the odd man out.  If you aren't using Zamp panels, it is a simple thing to switch the wires to opposite terminals.  

Good question Lisa and one we should have answered long ago.  I took the time today to call Zamp Solar and speak to their technician, Jesse who spent some time and gave me a valid reason for the way Zamp designs their solar panels.  The reason Zamp wires up the panels the way they do is to protect the panel itself.  If the "male" plug end coming from the panel were bare, this could cause a short circuit condition in their solar panels if the "exposed" positive end made contact with a grounded surface.  So in effect the "female" (negative) end of their solar panel plugs are exposed and bare and this eliminates the potential for a short-circuit situation should someone touch the bare end to a grounded surface.  

To cure the "reverse polarity" situation you certainly can flip the wires on the Zamp Solar connector, but the real problem originates with the Battery Tender plug ends that are reversed from Zamp's design.   First of all Jesse explained to me that the Zamp Solar port was "specifically designed" for Zamp's solar panels and was never intended to be used in conjunction with a Battery Tender.  So therein lies the real problem (the Battery Tender units) and rather than have the "bare end" connector issue Zamp chose to shield the positive side of their panel.  

A more permanent and quicker resolution to the above issue might be to cut the supply side line leads of the battery tender (the charge wires coming from the Battery Tender unit to the trailer battery), flip them around and splice them back together (if you are knowledgeable in splicing, electricity, etc.) so it matches Zamp's design.  By splicing out the Battery Tender wires it becomes a permanent fix as long as you remember this should you use the "clamp type" (alligator clip style if you will) connectors supplied with the Battery Tender.  If you don't, you could end up placing the wrong leads on the battery and creating a short circuit that way!  

Zamp does sell products for the specific issue above and Jesse will email me some information later today that I will post up here on the forum.   Their explanation makes perfect sense and the light switch suddenly went on once I heard their reasoning.  

Thanks for asking!  

There's never a stupid question here Jenn!   I don't see any issues with that Jenn if the polarity is correct and cable size is similar.  Your performance should be the same if you're not running a mile of cable from the panel to the battery.  

Hi Mike and Jen,
I just ordered a 12 ft extension cable from Deltran. You guys think I could just do the splicing and reversing on the extension cable and the charge the batteries by way of the Zamp port?

dundons said:

Hi Mike and Jen,
I just ordered a 12 ft extension cable from Deltran. You guys think I could just do the splicing and reversing on the extension cable and the charge the batteries by way of the Zamp port?

Yes, and as SeaJeeper noted as long as the polarity is correct when you splice out the cable there will be no issues.  Just trace the positive/negative wiring back on the Zamp solar port on your trailer tub and splice the cable out accordingly.  

I don't have quick access to verify the battery charging wire setup .... but wouldn't it be simpler to trace wire from inside of tub and swap the polarity as it connects to the battery... unless the charge wire coming from the wfco or vehicle is connected to the same battery leads... if you are mixing the polarity of devices as it connects to the zamp port then it makes sense to adjust to a comon polarity for the zamp before it attaches to the tub... i am not fond of cable splices exposed to camping weather conditions

I just drill out the lead so it fits both terminals... if u are not using mixed polarity swapping from both zamp and not zamp based equipment then it would be safer and simpler to swap leads... just consider the next owner of that tab wouldn't expect that configuration and on selling would be advised to revert to factory polarity.  As I said if you are not dealing with different polarities for the devices attached to that port then you are best off to not damage to cable supplying power and allowing for moisture to ground out through a wet splice

Just a bit of information. I called Zamp technical department and asked about the reverse polarity. Their answer was ' It's an Internet myth'.  I didn't reverse any wires on my solar system and it works fine. 

Yep, if you want to use a battery charger via the Zamp outlet, you need an adapter, too.  

Yes, as soon as I can look it up.

@Michigan_Mike, Will this thing do the trick of reversing polarity? 
http://a.co/dvy8njx

http://www.solardealz.com/Sidewall-Port-Adapter-for-Plug-N-Play-Maintainers-p/zs-bdc-adpt.htm

I use this adapter to hook our battery tender to the zamp port 

dundons said:

@Michigan_Mike, Will this thing do the trick of reversing polarity? 
http://a.co/dvy8njx

Good find!  

Updated link for the adapter, battery tender to external Zamp socket. Free shipping as of this post.
http://tincansolar.com/product/zs-bdc-adpt/