Generator 12v chargeing

Would I be correct if I assumed that this 12 vdc charging circuit you refer to is the generators cranking battery charging circuit?
If I am correct in assuming this, Then I would say it is not a good idea. It would be wiser to purchase and install an inverter/charger such as the Trace DR 1500 for example.

The Trace (Xantrex) DR 1500, among others, has the built relay(s) and electronic controll circuitry that allows pass through vac power and regulating a charge to the battery bank while the generator is burning fuel. When the generator is not burning fuel the DR 1500, among others, is making vac from the vdc on demand and it has an adjustable idle mode.

This may not be the less expensive course in the here and now but thats renewable energies for you.  the renewable energies industry was not created to save us money. It was created for the same reasons as any other industry, profits. We are just supposed to believe that its okay to spend more for RE because we are "saving" the planet Earth in the process.

The RE industry is really no different than any other industry, its bottom line is profit. Whats more, if you read the news articles concerning RE there will most assuredly be a mention about government (taxpayers) money involved with R&D or incentives to create or incentives to buy. Talk about paying for something out of more than one pocket.