LiCoO2 / NMC aren't the popular chemistries any more. LiFePo4 is a remarkably stable chemistry, with extremely low risks of fire.

In the unlikely event that they do catch fire, they are extinguishable with water.

Nothing has zero risk, but there are much more stable chemistries available than those that formed this (rational) opinion.

That's reassuring to know, thank you for pointing that out. I didn't get the impression this was already solved since you still keep hearing about battery fires, but hopefully this means that will be a thing of the past soon.

I would still skip this step and let it be the power company's problem though, simply because at ~400 USD / kWh they don't seem very cost efficient for off-peak storage (at least in my country).

To be sure, they're a cost -- but at least in America, LiFePo4 batteries are practically being given away right now -- 100Ah@12V for ~$100 US. I suspect these are the "let's make hay before the tariffs hit" prices, but there are a lot of unpronounceable brands making surprisingly high quality products in the space.

As for off-peak storage, these would allow you to replace a Tesla powerwall for ~$600-750 US. I don't know your country, or its peaks (or valleys) but on my sailboat, off-peak is night time or cloudy days, and in sunny climes, 600ah gets me nigh infinite power. Without clear skies, I'm limited to ~4-5 days of normal consumption.

(Not trying to nudge you off your position at all, just sort of reflecting/remarking at how practicable this all is at the moment.)

I can order 2kWh of LiFePo on Amazon for 500€. Are batteries that much more expensive in the US?

Look into LiFePO4 batteries