Best trailer battery kit?
 

I'm looking to put a winch on my trailer and will need some sort of battery to power it. It would be nice if the battery was charged from the truck towing it while plugged in but IDK if that is how it works or not... What are my options, oh sage trailer gurus!

It depends on what you want tow (weight) and how long you want to tow(time).Batteries will be killed very quickly if you don't recharge them as soon as you discharged them.
The second thing to have in mind is the extrem heavy current drain.
It will kill the battery if the battery is drained more than 50% which is about 12.2V. Most pople think when the lights dim the battery is empty- this is not true.It is already in a deep discharge state which will decrease your life span of the battery.

So you would need a heavy (or better called huge) deep cycle battery--->expensive!and of course some thick and expensive cables to recharge and connect the battery.
What about a HD come along? or those hand operated winches? Reliable, healthy (been looked at it from the sportsman side)and cheap?

But first you should know about your to-be-towed-weight...

My cousins trailer is set up with a winch. I believe he has 2 batteries (could be one) hooked to the winch and a constant charge off the 7-way plug off the truck when it's plugged in.

It's a 3k lb winch that I have lying around. It would be used only if a rig is broke enough not to get on the trailer under it's own power. The length of the deck is just shy of 20' and the ramps are 5', so 30' max pull onto the trailer on a rare occasion...

Might want to invest in a bigger winch. I wouldn't use that 3k on anything but an ATV or smaller.

That sounds like the set-up I would want! Any more details you could give?

I will look for a chart for rolling resistance and incline telling you exactly what kind of GVW of rigs you can pull with that winch. If you are willing to run the trucks engine while pulling and to invest the needed battery cable and connector I don't see any problems with using that winch. those hand operated winches to pull boats are much weaker and being used on passenger car trailers too.

I don't, but I'm sure someone will have some insight. I believe you'd want one of these though http://www.atkinsonelectronics.com/p...s/TBCM-40A.pdf

If need be, I have enough cable to run a snatch block on it. It will be more than enough for what I need and it will be free!

I like that! I would love to find that included in a full kit with a breakaway... (Not that I think my pintle set-up is going to come loose!)

That relay will burn off.
Why?
1. Kirchhoff's knot rule applies: sum off current flowing in equals sum off flowing current out.
The winch will demand a lot of current and has two sources. battery and supply cable. If battery current diminishes all current possible to get will be sucked from the cable. The cable will resist and get hot- the next weak part is the relay. Expecting damage is guranteed if you don't disconnect the connection,:w2:

As I told you I looked for pulling weights
you have to divide towed vehicle weight by:
50 if you tow on road
10 if you tow on grass
5 if you tow on gravel
3 if you tow on sand

you also can calulate the inclination of the ramp with:
towed vehicle weight divided by 60 and multiplied by the inclination in degrees.
I hope this gives a general idea about the abilities of your winch(as you mentioned already you also can use a snatch block).