Inverter

Where is it connected to the trucks electrical system and what gauge of wire is connecting it?
No inverter over 500w should be plugged into a cig lighter outlet or connected with less than #12 wire. Up to 1500w can function reliably with #8 wire. Anything larger should be connected directly to the battery box with minimum #4 cable and fused at the battery box. All connections over 10ft wire run go to the next size larger wire/cable.
Also clean your battery terminals and ground connections at least twice per year (I did mine the weekend of the solstices) the dash gauge reads alternator output not battery condition while running, it reads battery output with key on not running only. 13.8v to 14.2v is standard alternator output, 12.4v to 12.8v is battery condition not running. Any not running reading less than 12.1v is normally due to poor battery condition or poor connection.

 

ok you need your inverter hooked up with one wire on one battery and the other on the battery beside it. no it will not give you 24 volts as you have a bus bar on all your batterys to run them together to give you 12 volts. things is the only reason your getting 11.5 volts on the inverter is you got it wired to one battery thats not how it works. it has to run off the system to work. do not run your inverter without a apu or the truck running. it will ruin your system batterys included. zero gauge wire is fine. problem is how you have it wired in

 

What is the inverter rated at?
How many watts?

 

Should be big enough to power anything you can plug into it.
Two things I have experienced with lower voltages than expected:
- alternator had burnt rectifier on one of the phases, it seemed to put out proper voltages at low loads. When a heavier load was applied (my microwave or all the lights at night) then it showed low voltage.
- bad cable or crimped lug, wire had an oxide coating on it that insulated the copper from making a good contact with the lug that was crimped onto it.