What do you use as a battery tender when parked for long periods?

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Wanderlost

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I'm looking for a method to keep our house battery fully charged and maintained when the vehicle is sitting in the garage for days or even weeks at a time.

We have an AGM with a Redarc dc-dc charger with built-in solar controller. What I'd like to do is have something I can plug into the garage wall outlet then into the solar input plug we have for our portable solar panel. Is that possible? I'm trying to make it as simple as possible to plug and unplug, no opening of the hood if I can help it.

Any ideas?
 

Road

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Hey @Wanderlost, what I've found to work really well for keeping my dual AGMs topped off while not in use, is to just keep my portable 120w folding panel hooked up full-time when parked.

I realize your vehicle is parked inside. I made a couple heavy duty extensions for my panels. Using a good heavy gauge of high grade stranded tinned copper wire minimizes loss in the run.

If my batteries were in a vehicle or trailer parked inside, I'd find a good all day spot for the panels, hook 'em up conventionally using my extensions, run the cord under the garage door or even make a dedicated port through a wall, and let it work with no worries. Then you have great cord to use when camping, too, if you move your panels around a lot. I'm almost fanatical about moving mine for optimum input throughout the day, and depend a lot on the power I store from my panels for when camping backcountry for weeks at a time.

solarcable_0373-900.jpg
I made my extensions into manageable lengths so I can do multiples of 25' as needed, depending on how far out I want to go with my panels.

Long extensions are easy to make. I have several and made them right in camp. After using a variety of wire over the years for extensions and growing tired of it being too stiff and unwieldy when coiling and storing, I've settled on using 10AWG Silicone highly stranded tinned copper wire.

cable-camp-workshop_9871-900.jpeg
In-camp workshop making a couple heavy duty extensions. A good wire crimper is essential for crimping the terminal ends in the Anderson connectors. It's a tool I now carry in my tool roll full-time.


solarcable_9905-900.jpg
I used the home-made extension on the right for a long time, and keep it for when I want to go even further out with my panels. Too stiff and cumbersome for regular use.
The cable on the left, also home-made, is far superior. It is 10AWG Silicone, highly stranded, super flexible, and very efficient compared to solid wire.


andersen-sae.jpg
Don't know what kind of port you have going into your charge controller, but you can get the ends easy enough and make a pigtail with an Anderson connector so you can run your extensions. Mine is SAE, so that's what I use, though I added a fuse in the pigtail.

For long term parking, I've been pleasantly surprised at how well it works without moving my panels at all. I keep my panels flat, on top of my hardshell RTT on my trailer, hooked up to the charge controller full time. I actually let it keep my diesel van's duel batteries topped off, too, by leaving my van hooked to my trailer when parked. There is enough 'reverse' flow through my 7way trailer hook up that even on the coldest of days after sitting for weeks without starting, there's more than enough juice to start the ol' girl.

solarsnow-210213_4986-900.jpeg

It's one of those things I sort of kicked myself for not realizing sooner; that I could use my panels to keep all four batteries topped off and not depleted. Hook it up and leave it. I used to keep my panels folded and stored when not camping (trailer batts would deplete over time, parked long for the pandemic), and would run a long extension cord with trickle charger to my van any winter night before I knew I would use my van.

I've used this set up since autumn. Now, even with the panel not in prime all day sun, and even though flat and not moved or angled for the sun's position at all, I've been floored at how well it keeps all four batteries topped off.

I keep track of my batteries condition with a simple Innova battery monitor plugged into a 12v outlet in my dash, angled so I can see it without opening the door, night or day. I plan on installing an external 12v outlet on my trailer so I can use it there, too, to check my trailer AGMs separately without cleaning off ice and snow and opening the nose box lid over my power center.

innova-monitor_5053-450.jpeg . innova-monitor_5051-450.jpeg
Best little investment I've made for checking battery levels.


PowerCtr_9429.JPG

Long-winded response, I know, though I hope it helps lead you to a solution for your needs. It's a piece I've been meaning to write all winter for my blog, and your query prompted me to put it in order. So, thanks!

- Road

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Last edited:

DMS1

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On my RV, I use 4 HF 1.5 watt solar panels connected to a Battery Tender 5-45W Automatic Solar Controller. The Solar Panels just sit on the dash. I am going to be setting up something similar to my 4Runner now that is has to be parked outside, currently looking for a compact 20 watt solar panel that will fit on the dash.
 

old_man

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While a trickle charger is nice especially in subzero temps. I go out and start it up every few weeks and let it warm up and get the oil circulating.
 
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Wanderlost

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Thanks for the replies everyone!
We decided to go with a simple plug-in trickle charger for the time being. We'll be working on a permanently mounted system that we can simply plug into.