Question about a supplementary AC to DC charger.

I have a 1.6kw RV solar setup with a Victron Multiplus-II 120x2 and 810Ah of Lithium batteries that I use off-grid often. Most of the time the solar is more than sufficient, but I have a backup inverter generator that can do 3kw sustained load if it's cloudy or if I need to run air conditioning. I plug the generator into a 30A RVs shore power cable, which runs directly into the Multiplus AC in.

The system works well, but when I need to top off my batteries with the generator the 120A charger on the Multiplus + base loads ends up only drawing at most 2kw. I'd like to use that extra 1kw of generator capacity 1) to charge faster and 2) because I'm assuming it's more fuel efficient to run at closer to full load rather than half load. So I'm looking for a good option for approximately 80-ish amps of AC to DC charging, which I can hook up to my Lynx busbar. I'd like to stick with Victron products if possible, so that gives three options I can see:

1. Skylla IP65 12/70
2. Centaur Charger 12/80
3. 3x Blue Smart IP22 12/30

The first two options seem to be very capable, but also very expensive. It feels like they have more design options than I need, and I'd rather not pay 800+ USD for these unless there is a very compelling reason to do so. I can find the 3x Blue Smart 12/30s for ~600 USD, which is still a lot, but at least better. They also seem to take up less space than the other two options. Honestly, if I'm spending almost 1000 USD it seems like it would be better to get a second Multiplus-II for the extra charger and inverter capacity, but sadly I don't think I have the space for it.

So I have questions:

1. Does anyone have a recommendation as to which of these three options to use for this project? Pros/cons of these choices? Will they all integrate into my current system equally well?
2. With whatever I end up using, would it be better plug it into the AC system currently on the trailer through the panel and therefore Multiplus, or run a dedicated supply cable from them directly to the second 20A AC outlet on the generator?
3. What advantages am I gaining by spending 4-6 times more on a Victron-specific option here, as opposed to something like this: https://www.amazon.com/gp/product/B0CGTM9SQ6/

Solar_Sam said:

1. Does anyone have a recommendation as to which of these three options to use for this project? Pros/cons of these choices? Will they all integrate into my current system equally well?

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I assume you are at 12V. If you were at 48V I'd recommend the Chargeverter (100A for about $400) but at 12V I'd go for a simpler solution, like a Meanwell power supply. A Meanwell RSP-1000-15 (trimmed down to 14 volts) will give you 50 amps at 14 volts for about $270. There's no three stage charging, but for occasional use it's reliable, small and cheap.

Iota, Samlex, and Aims offer low cost multi stage chargers

Id probably try the Aims. Its 70A and adjustable so you can turn it down if you happen to overload the generator

Solar_Sam said:

I'd like to use that extra 1kw of generator capacity 1) to charge faster and 2) because I'm assuming it's more fuel efficient to run at closer to full load rather than half load.

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Efficiency above 50% load is generally very flat. It's below 40% load that efficiency drops away. For some generators efficiency drop as you approach 100% load. 2/3rd to 3/4 load is generally pretty good sweet spot.

By going close to 100% I think you'll just burn more fuel and charge faster but not really gain much efficiency bonus.

Best to run generators at max 80%. 50-75% is a good range.