So...
I went down the rabbit hole on this. Seems interesting, as I'm paying 11.2 cents per kWh (vs. their 8.5). They do mention they guarantee you to have a minimum amount of power in the batteries, but it isn't 100%.
One thing that is in beta testing is this:
https://help.basepowercompany.com/en/articles/11914967-how-do-i-use-the-generator-recharge-portEssentially, you have the batteries and an ATS to power the house (exactly like a backup generator, but batteries instead). BUT they also have a plug on the side to hook up a generator. So during the day, you could run a larger generator, fill up batteries AND run the house, then disconnect generator at night and run house on batteries till the morning. Technically, the generator could be any power source: panels OR genset. So you can stretch your gas storage (potentially) because the generator is running at 100% to run house and fill batteries then turn it 'off' when batteries are full.
Something else to consider is this brand (again, rabbit hole).
https://us.ecoflow.com/products/delta-pro-ultra-x?variant=54714781171785This is essentially a back-up battery for the house (same as above), but you treat it like a generator. Can plug into a breaker interlock or wire it in to an ATS and power your house. This brand (ecoflow) has several things that manage the power usage in your house as well merge a breaker interlock or sub panel into the main panel. Pricier, but the advantage is that you aren't dealing with gasoline or generators. Nor selling to the grid.
But with the Eco, you can use a generator or panels to charge batteries during the day (or genset at night) and still use the batteries other times.
I've emailed to ask about using the link I put above as a genset on a breaker interlock. So if I lose power, I flip a couple of breakers, plug the rack in (4-5 batteries) and my house has power again. I can charge batteries with solar or genset at the same time, but I'm not getting a permit or telling Centerpoint I have an ATS.
edit: I don't own anything nor rep any company. Just some examples I found online.
~egon