New shed setup, sanity check

[MisterSandals]

I'd appreciate a little help with this calculator, I don't know what those input parameters mean except size and distance.

What amps, volts and distance is your example? I can provide populated link with result.
If you have a preferred wire size, we can see what the voltage drop would be.

 

[MisterSandals]

Know anything about this brand?

No but that's not saying much.

Google search on "UPS12-400MR battery" shows quite a few respectable-looking websites...
and a glance at prices are $200-275 for new.

Craigslist ad for 3 years old, no warranty, half price.

I dunno.

 

[trupper]

What amps, volts and distance is your example? I can provide populated link with result.
If you have a preferred wire size, we can see what the voltage drop would be.

I have no wires at all, so I will purchase whatever is required. I will also round up to be safe. I see 4awg is used to connect the batteries in series, the wires are short, so I thought it would be sufficient, but from there to inverter and controller it will be about 3-4 feet, I'm lost. In my new diagram the battery will put out 24v.

 

[MisterSandals]

but from there to inverter and controller it will be about 3-4 feet,

I hope you mean from the battery to the inverter!
So using your numbers and the voltage drop calculator:
12.8V, 4', 2000W/12.8V = 156A

Here is with 4awg ... comes to 3% voltage drop so 4awg is too small

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

Testing with 2awg comes in at 1.96% voltage drop (acceptable, still need to verify wire ampacity):

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

 

[trupper]

Thanks so much for all your help and patience! I will now play with it and figure it out