Severe battery drain on start-up

Sounds to me like you have one or more batteries dead. I'd recommend getting them load tested.

 

Swing by my house. I just bought a 500 amp carbon pile load tester and want some questionable batteries to try it out on. No Charge!

I mean Free! I will give ya a charge if you need it to get ya going again.

 

Could be lots of issues. If it cranks quickly its not batteries. Best is to get out a volt meter and check voltage at various spots while cranking. Don't do anything until you do this.

 

If you haven't done so, get some jumpers and ensure you've got all four batteries in parallel... I know on our KWs, the four batteries are separated into groups of two... the forward two are the ones tasked primarily with cranking... by running all four in parallel, you retain the same voltage, but you have more available amperage.

 

First off you want to disconnect the batteries and independently charge them one at a time, with a regulated charger, clean the cables, the connectors at the starter, inspect every cable for wear, loose ends, and to the block also the cab ground. protect them with dielectric grease. Then, check the voltage of each battery. They have a computerized battery tester that works great. You want a voltmeter with a MIN_MAX feature, press the button and start the truck then press the button again it will tell you the minimum battery voltage needed to start it. you should have 10 plus volts. I have a clamp meter that measure the amperage used to start it, from memory 400 to 500 amps is OK above that the starter is getting suspect.
Just a thought!

 

Any truck stop with a shop should be equipped to do the battery test. It's not a complicated process.