Thanks, it's about 7 inches on 37s. Yeah, I just tested my batteries and they are both good. We are having the same exact problem. I hope we can figure this put. When you see if that's the problem let me know. You can text me at 8158787864. And post on here. Im texting for a draw tonight. And getting my alternator tested. Plus I'm Gunna wire up a new voltage regulator for the he'll of it

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Heres an update. I Charged batteries overnight. Load tested good. Unhooked the grid heater lead wires at the battery. Fired up the truck. Volt gauge immediatly moved to 14v and stayed there. Hooked up the multi meter top the batterys. And the out put of the alternator. 13.99 volts. So it'd charging just fine. I think the grid heaters are the problem. It only did this once it got cold. A relay has to be sticking or something after it shuts off or something. I think we can point the problem at the relays

 

my truck is doin the same thing too. if i run it every day it'll start fine, but if i let it sit more than that, it wont crank fast enough. i'll have to try unhookin the grid heater

 

i unhooked the grid heater at the heater itself and it sat from about 4'oclock yesterday till right now.. it cranked over pretty well but didnt start.. prob because it is cold and i dont have a grid heater.. but i am going to fully charge the batterys tonight and put them in 2maro morning and leave it sit again and see how it works.. the batterys were completly dead yesterday and i jumped it and drove it for a few minutes but they were still low. so i will charge them through the night and see how they do. and i will text you or post any updates.

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Switched Grid Heater another idea

 

I unhooked mine. I'm Gunna let my truck sit for a few days then check the voltage with a multi meterbefore I even crank it over

 

i bet its the solinoids sticking

 

if yer battery voltage gets low the grid heaters will click in and out like that because not enough voltage to hold them in

 

Switched Grid Heaters think im gonna do this if this is the issue

 

I bet it is to. I unhooked them right from the battery. I'm not Gunna try starting it or test the voltage till monday

 

It might also be your battery terminals. They could be bad and not making a good connection. After a truck being worked on and having those terminals being tightened and loosened throughout the years of the truck being the terminals could get corroded and messed up not making the best connection anymore. My truck cranked REALLY slow and some days the first start of the day on a cold morning it almost seems like it wasn't going to start. Finally figured out even though my terminals were tight, the connections was bad. Only really cranking off one battery, barely. Bought some marine terminals from NAPA and starts quick every time ever since! AND if you get the marine ones, and put battery cable lugs at the end of the cable, you wont have to always take the terminal off when working on your truck, just lossen the wing nut, and your not powered

 

Maybe Duralast batteries last like Duramax trucks