Batteries went dead bought 2 new and checked for a short have a 12 volt short.

It sounds like an alternator related issue. Once the battery drops below 12 volts it will do lots of silly things with gauges and thats why when you change it all works fine. Check that with engine running with a volt meter you have 13.8 to 14.2 volts across the battery, if not you may have an alternator issue

If you have 4 off 12 volt batteries connected in series (positive to negative leaving a positive terminal and negative terminal with no wires on then that is 48 volts. To check the batteries you have to disconnect each battery and have a load test done on each battery for 12 volts and dead cells. To get 20 volts you still have 2 batteries connected together with a good battery connected to a battery with a dead cell or else you would have 24 volts.

You have dead short in your system draining the battery.
Unless you have a place where the truck was wrecked and the wires were pinched causing a short circuit, the other thing that often causes this is a short in the alternator.
God bless your efforts to find the problem.,.l

A voltmeter is NOT the correct tool to check for an "ignition-off draw". A voltmeter will show 12 volts if ANYTHING is operating.

There are some things that are SUPPOSED to keep operating when the vehicle is shut off. These include, but are not limited to:
> Powertrain Control Module keep-alive memory
> Radio preset memory
> Clock
> Security/ alarm system
> Remote control recievers (door locks, etc.)

What you need to know is how many AMPS are being drawn from the battery when the vehicle is shut off. This is done by using a shunt bar connected between the battery terminal and the battery cable connector.

Set the ammeter to the lowest setting (usually 2 or 5 amp scale) Connect the ammeter leads accross the shunt bar. Turn off all electrical accessories, ignition switch, etc. and wait for a minimum of 45 minutes for all of the computer systems to go into "sleep" mode. Then open the shunt bar and read the amperage.

The "rule of thumb" is 300 milliamps (or 0.3 amps). This is where you have a problem. Anything less than this is not a problem and is not the cause of your dead battery. My experience is that most vehicles built in the last 15 years or so, will usually measure around 150 milliamps if there is no aftermarket equipment installed. Please note that even this 150 milliamps will measure as 12 volts if measured with a volt meter. A 2 amp draw will also measure as 12 volts....However, a 2 amp draw will kill your battery overnight and the 150 milliamp draw won't.

Sounds like dead battery check battery voltage with a multimeter it should read between 12-12.6 volts anything less than 12 volts you'll need a new battery.

You need to get a volt meter on it. Your battery should be around high 12 to 13 volts while not running, and increase a little without going over 14 1/2 volts running.

Have the alternator checked,or you can check the out put with a volt meter.Attach the volt meter to the battery,it should read,13.65,to 14.25 volts,if it is lower than this,the alternator is not charging.

buy a cheap volt meter check voltage on both sides of the starter seleniod on the fenderwell if you have 12 volts on both sides while cranking test voltage at starter if you have 12 volts at starter with fully charged battery and it doesnt start you will need a starter it also sounds like you might need an alternator once you can get it started

Make sure you have 12 volts from the positive side of the battery to the starter. Check the small wire on the starter solenoid and make sure you have 12 volts when cranking engine. If voltage is correct, the starter is bad

short or loose connection