Found a test document for the full system those batteries are designed to go in... 1088 volts nominal!
https://www.murrumbidgee.nsw.gov.au/files/Battery-Test-Report_PAN-92189.pdf
This battery is a lot larger than the 100ah mini. The dimensions are 15" long, 7.5" wide and 9.65" tall. I kepworth told me they are using prismatic cells. The battery box dimensions are similar to the DIY box for the 280/300ah cells.
It would be a little less efficient but much cheaper since all he would need is an extension cord connecting the truck inverter to the trailer. A DC-DC charger + cabling, fuse, etc is much more expensive and you're still somewhat limited on charging current without adding even more DC-DC...
From Amazon: "Please contact the seller directly for warranty information for this product. You may also be able to find warranty information on the manufacturer’s website". I couldn't find a website for NewtiPower.
I am designing a battery for an RV that has a pretty small battery box. I'd like to figure out what the max capacity (24v or maybe even 48v if possible) I can fit in a box this size:
Length 17"
Width 13"
Height 15"
I'm pretty sure I could fit 8x of the 304ah prismatic cells for a 7300wh...
Just something to consider: EFI can have its drawbacks too. More complexity = more stuff to go wrong. Fuel pump, various sensors for the EFI system, injector, etc. What are the availability of those parts if something goes wrong in 5-10 years? Carburetors are very simple and easy to fix even far...
I have a setup similar to your diagram but use an automatic transfer switch. I wired the converter to the shore power input side of the transfer switch so it only comes on while connected to shore power.
I sure wish they had an isolated version but otherwise looks good. I like the IP65 rating as I'd love to mount this on the underside of my camper as I have very limited space available inside.
I emailed kepworth and they said that for two they would be $495/each shipped and that they had them in stock in the US. I replied asking for more details like cell type/brand and what kind of BMS it has but I haven't received a response to that question yet. Super tempting at this point but...
I would test your batteries with your expected loads before spending a lot of $ changing them out. Hobotech did a pretty thorough test of that battery and was able to sustain 150ah discharge for 5 minutes. In theory to support 3000W each battery needs to support 125A which will probably be fine.
My charger is not connected to the panel at all. The input is connected to the shore power side of the transfer switch and the output goes directly to the battery bank (fused of course).
That air conditioner is $2800 and still pulls 800-1000 watts of power. You're still going to need a LOT of battery to run that for any decent amount of time and then you're going to need a lot of charging to get that battery topped up again.