Balmar website has a page where you can estimate the size of the alternator and, with 640 Ah of lithium batteries, you need a really big alternator or two alternators, but I've checked how much cost the Volvo arm, Volvo pulleys, cables, relay and so on, plus the second alternator 100A, and it's at least the same price as the Balmar.
Of course the other option is to wait for hours and hours with the engine running, but I bought a sailing boat not to hear the engine.
I have big solar panels and I try to keep the consumption as low as possible, but nowadays with automatic pilot, microwave, induction cooktop, electric winches, etc. No windlass yet but will need it sooner than later.
So my conclusion is that I prefer to have electricity in excess rather than the opposite.
What scares me more from the Balmar option, besides of the price, is that I send a couple of questions to the customer service and no answer yet. Being such an expensive piece of equipment I would expect better service. Definitely I don't want to be one year like Jeffatoms2 to solve all the problems. Specially if I'll need the help of a professional which is not a Balmar dealer.
