Current Draw on System

Make sure key is off and all constant power accessories like CB, inverter etc are off. Then just disconnect the negative cable from the battery group to the frame. Use the ammeter function of a multimeter and use the meter leads to complete the circuit where you disconnected it. If it reads ballpark 350-450 milliamps I wouldn't worry too much. Computers are always going to draw a small amount of power.

Wouldn't really waste my time doing voltage drop checks on the cables if its starting fine and the batteries are getting around 14 volts with the truck running and all lights/accessories on.

 

I get .4 out of positive and .25 returning from negative. With no kill switch. It might drop with truck fully asleep but I'm not waiting however long that takes.

.15 draw.

You can buy a induction clamp Amp meter. It clamps around the cables. No need to disconnect cables.
They have an arrow on the clamp to indicate current direction. if the arrow points to the battery on positive it reads negative. Arrow away from battery it reads positive. On the negative it's opposite. Arrow to the battery it's positive. Arrow away from battery it's negative reading.

You need something that reads DC amps. Most are AC amps. You can find em cheaper on Amazon.

https://www.harborfreight.com/cm610a-600a-t-rms-acdc-clamp-meter-64015.html

Positive always pulls more then negative returns.

 

I found an easy way to tell if a draw. Remove the + cable, put a test light from the battery terminal to the disconnected cable, if the light lights, you have a draw. Start pulling fuses until the light goes out. The truck shouldn't lose any power when off.

 

Check all of your grounds.

 

And have the alternator checked including ripple (amount of ac current passing through the diodes and not being converted to dc current).

 

One way to get a hint on alternator problems is to let the truck sit overnight so all is cool.The next morning put your hand on the alternator before starting the engine to feel if it is warm. If it is you may have a problem with the diodes.

 

the test light only works on NON computer vehicles.

Today's vehicles have computers and radios that maintain information and require power. There's always going to be a draw.

 

Well, that sure dates me, huh? Those things wouldn't drain 4 batteries overnight, however.

 

Depends on the condition (or age) of the batteries. Brand new. No.

I started the truck one day and went to work. At the end of the day a guy was wondering why my truck stunk. I can't smell anything since covid. But I thought he was smelling the weed burner exhaust. He didn't say anything about a rotten egg type of Sulphur smell. When I parked the truck I could hear an air leak. Inside the box only. I measure the volts after truck off. 13 volts. 12 hours later i came back to TWO volts. One battery drained all 3 batteries.

It should be noted. That dirt is a conductor. And will also drain the batteries if not kept clean.

Use a voltmeter. Negative on post. Run the positive along the top of the battery. And watch the voltage readings. It don't take much dirt to show full battery voltage.