Sine wave 3000w go power inverter

[treegump]

Got a new fleet truck that has a 3000w inverter vs a 3k or 5k generator to power our darkroom. It can't keep up with the dryer and a/c or heater and a/c. A cable runs from the engine to the back, and than goes to 2 cables connecting to 2 6 volt batteries (the size of car batteries) which are hooked in series to make 12 volts before going to the inverter. I tested the batteries last night after driving home, and they tested 6 volts each with the voltmeter. Than I used a battery tester, which showed "bad", but not sure if it's supposed to be for just 12 volt batteries, or not. *Also, truck doesn't have high idle, but it seemed to do decent when we shoved a stick on the pedal at 2500 Rpms. (2010 k2500 6.0)

So, does it sound like bad batteries in back? Also, is their an advantage of have 2 6volt batteries in series to make 12 volts, verses having 2-12volt batteries in parralel?

 

[NVW]

A lot of farm equip. uses two 6v batteries in series, they have high CCA's. To test them put the tester on the bats hooked in series, it won't test them individually that way but will give an indication of the pair.

 

[treegump]

Why not just get 2 deep cycle 12 volts and have a greater quantity of stores voltage?

 

[orrum]

The six volts hooked that way can be recharger more times than a deep cycle marine. My dad switched his rv that way but a two sets for a total of 4 batts, when one set went down the thing switched automagically.

 

[racedaymechanic]

The six volts hooked that way can be recharger more times than a deep cycle marine. My dad switched his rv that way but a two sets for a total of 4 batts, when one set went down the thing switched automagically.

????