If u have a multimeter disconnect a battery terminal, set the meter on 10a hook one to battery and other to terminal. This will tell you how much parasitic draw you have .05 is the absolute max, it will take a cpl mins after hooking up for the CPUs to go to sleep if its over which I'm sure it is start by unplugging any aftermarket devices one at a time until u are below .05. If no Change start at fuses, but more times then not its aftermarket, alarms, lights, and what not, start with most recently added devices. You can pick multimeters up at any parts store or harbor freight for under $20

 

Nothing has been added to truck since plow was added. I will have to get the multimeter.

 

load test your battery, just because you replaced it doesn't make it perfect, loose terminals, something loose somewhere

 

Unplug your plow for the night and see if it starts the next morning. If so "Bob's your Uncle!"
I had an mercury switch on my underhood light go and the light stayed on and drained the battery, my wife was walking by the truck one night and saw the light on the ground underneath.

 

What happens if you unplug the plow?
You can also use a test light instead of a meter

 

replace your battery cables...just had a buddys doing the same thing and ground cable was corroded inside the insulation

 

Unplugged plow over night. Just tried to start and it dead.

 

Do you have a test light?

 

Do you have a test light?

No I will have to get one. once I have what do I do?

 

Parasitic draw test

 

Take negative battery cable off. Put test might in between cable and post. If it lights up you have draw. Pull fuses until light goes out

You can also use a bulb

 

Take negative battery cable off. Put test might in between cable and post. If it lights up you have draw. Pull fuses until light goes out

You can also use a bulb

X2 do this test!

Just had a problem like that when cold with one of my trucks, 06 F-350 6.0.

Truck would not start when in the teens, got worse and worse. Did all test as mentioned above, along with load test batteries, both of them separate on the truck and on the bench, they both tested good.... fast forward, bought new battery's and problem was solved. Even the batteries "test" good, from my experience they can still be bad.

 

I put a rebuilt alternator in my truck 2 years ago that had some sort of short in it. If the truck was running it would work fine and charge the batteries and work as it should. If the truck sat for a day or two batteries would be dead and truck would need to be jumped, and would work fine again until it sat for a day or two. If you listened to the alternator with the truck off the was a quite buzzing/humming noise coming from it. I replaced the alternator and the problem went away.