Several years ago when the fifth wheel that I had at the time only had room for one battery, I carried 2 more in the back of my truck. I used 2 sets of good jumper cables with ring terminals on one end and winch connectors on the other end to supply extra battery power when dry camping. Fast forward a few years and my current trailer has room for 4 batteries so I do not use the cables like I used to. However, I got to thinking about using those same cables to charge my batteries using the truck. I would not be using it for hours to run everything but just a little while to top off the batteries in the trailer. Has anyone done anything like this?

Seen it often where folks use jumper cables from truck battery to trailer battery for a quick recharge. Theory is the jumper cables are shorter and fatter than the long skinny wires back to the 7-pin.Neither method gives you much of a recharge, but it can keep you going. Better to have a small generator and use your converter for a higher amp, faster recharge. Solar can sometimes help too.

It can certainly be done. Use good jumper cables right off your truck battery to the trailer batteries. The however in this case is your truck engine is producing a substantial amount of power just to run it's engine. A 2K generator will produce much less power and it's easier of fuel to run. The battery pack will take a charge at the same rate from both. One engine uses a lot more fuel than the other.

Seems an old fashioned and fairly ineffective way to charge batteries. A solar system will give you a faster and full charge.

I have been using one of those 10-watt Solar Panels sitting in the windshield area to trickle charge extra batteries when needed... When connected to my battery I can see my battery charge start out above 12VDC right away and will eventually creep up to 12.6-7 VoltsI think the MAX current is around 100MA or so which should not do any over charging of your battery...This certainly makes a difference if you are sitting for a long period of time and not running the vehicle etc...Google imageMine has these 2-pin connectors on it and I built up a lighter plug adapter so I can plug this solar panel into an always hot 12V Connector inside my truck... Great for trickle charging my truck start battery doing this...google imageI'm thinking this may be a great PLAN B thing to have around...You can pick these 10W Solar Panels up from AMAZON for around $40...Roy Ken

No. Your trucks batteries and alternator are not reallly suited for charging your trailer batteries. Get a solar panel and/or a quiet generator. Buy a long power cord for your trailer and you can run the generator in the back of your truck.

charging batteries with truck | Good Sam Community

32 Replies

S_Davis
Explorer
Jul 05, 2019
theoldwizard1 wrote:
pinesman wrote:
I got to thinking about using those same cables to charge my batteries using the truck. I would not be using it for hours to run everything but just a little while to top off the batteries in the trailer.

Modern vehicle (after about 2000) charging system work TOTALLY DIFFERENT than the past. They drop the voltage down to about 13.2V within a few minutes of starting. That is much TOO LOW to charge such a large battery bank !

This is not true at lest on my 2013 Chevy 2500HD, my voltage after starting goes to 14.7 volts for a few minutes and then settles at 14.4. I can drive for hours and it never goes below 14.4 volts.
MEXICOWANDERER
Explorer
Jul 05, 2019

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These are good for 50 amps @ 16 volts because I tested them and found only very modest warmth after a few hours.

The wires need to be soldered onto the mini-lugs on the other end. I would not hesitate to use 8 AWG with these plugs and sockets. Terminals are gold plated and the male bullets are X sliced so a thin screwdriver can spread apart the bullet to the point of making an insanely tight fit.

SEE (!) what you're missing by not taking a moment to learn how to solder?
2oldman
Explorer II
Jul 05, 2019
pianotuna wrote:
If there is a decent converter, consider powering it from an inverter connected to the battery of the tow vehicle.
Nice idea.
pianotuna
Nomad III
Jul 05, 2019
If there is a decent converter, consider powering it from an inverter connected to the battery of the tow vehicle.
SoundGuy
Explorer
Jul 05, 2019
pinesman wrote:
I got to thinking about using those same cables to charge my batteries using the truck. I would not be using it for hours to run everything but just a little while to top off the batteries in the trailer.

theoldwizard1 wrote:
Modern vehicle (after about 2000) charging system work TOTALLY DIFFERENT than the past. They drop the voltage down to about 13.2V within a few minutes of starting. That is much TOO LOW to charge such a large battery bank !

The solution being a DC > DC charger, one example being the CTEK 250SA. :B
landyacht318
Explorer
Jul 05, 2019
I had nothing but issues with those 12v SAE connectors. Too hot to touch at a constant 25 amps with 10 gauge leads. And forever intermittent after such use.
Go with anderson powerpoles instead.
landyacht318
Explorer
Jul 05, 2019
theoldwizard1 wrote:
landyacht318 wrote:
I found maxing out my alternator charging well depleted battery over thick copper when idling parked had my alternator quickly heat to 200 f+ degrees. But I can force.it.to seek and hold 14.7v.

What year, make and model vehicle and how do you force the alternator to seek and hold 14.7V ?

Mines just a dodge van with an externally regulated alternator. Tricked engine computer with a resistor and modified a transpo540hd regulator with an external potentiometer to choose any voltage i want it to seek and hold.
theoldwizard1
Explorer II
Jul 04, 2019
RoyB wrote:
Mine has these 2-pin connectors on it and I built up a lighter plug adapter so I can plug this solar panel into an always hot 12V Connector inside my truck... Great for trickle charging my truck start battery doing this...

That style connector has been around for a long time and they are quite robust. I don't like them for a couple of reasons.

• Frequently the two halves will not fully seat, leaving part of the metal exposed. Not tragic, but it just does not look right !
• You need two different halves if you are building something. Many times the wires are not color coded so you don't know if you have plugged in correctly or not
Lwiddis
Explorer II
Jul 04, 2019
If you aren’t fully recharging daily then your batteries will age fast. And not “some solar.” Do an energy survey of your amp hour use...or what you want to use...and start with adequate batteries, then at least one solar panel watt per battery amp hour. The total solar watts converted to amps determines the size of the controller.
theoldwizard1
Explorer II
Jul 04, 2019
landyacht318 wrote:
I found maxing out my alternator charging well depleted battery over thick copper when idling parked had my alternator quickly heat to 200 f+ degrees. But I can force.it.to seek and hold 14.7v.

What year, make and model vehicle and how do you force the alternator to seek and hold 14.7V ?

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charging batteries with truck

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