Warpspeed
Solar Wizard
Massively thick dc battery cable may not be necessary.But how else can one charge a large battery bank with DC charge sources when the battery is a 30 mtr total cable run from the charge source? Sure massively thick cables are one way, but it is that practical ?
The issue of course is voltage drop.
One solution to that particular problem is to use a voltage regulator at the engine end that uses remote voltage sensing.
The voltage regulator then acts according to the voltage measured directly at the battery, not the voltage at the generator/alternator end.
This requires a three wire (or sometimes four wire) connection between the battery and the voltage regulator. Two thick wires large enough to carry the main positive and negative charging current, and a third thin voltage sensing wire connected to battery positive.
The voltage regulator will then source an excess of voltage at the source that exactly compensates for voltage drop along both the positive and negative battery supply cables. This can be done with only three wires, because the regulator assumes equal voltage drops along both positive and negative, which will usually be the case. Four wire remote sensing is also possible if the regulator is designed to work that way.
The battery charging cables can then be made thinner and at lower cost. The resulting voltage drop will produce a power loss, but that may still be less than the combined loss of dc to ac conversion, and ac to dc conversion. You will need to work out some actual figures for all that.
You could still run a second inverter at the engine end, but you would need to ensure the dc voltage there will never exceed the maximum voltage input rating for the inverter. That is very likely not to be a problem, but must be checked.
This is the general idea:
https://www.delcoremy.com/alternators/alternator-features/remote-sense