Photovoltaic system offer for our single-family house

The cellar is ideal for the battery, if only because of the year-round temperatures there. Mine is also kept there. It wouldn’t be suitable for me in the garage; it can get very cold there in winter.

I believe that Snowy36 meant the fire hazard and does not want the source in the house (basement)

That was clear to me and certainly an argument. Without deeper technical knowledge, I would spontaneously suspect that the susceptibility to faults decreases significantly with good environmental conditions. At least in practice, I haven't heard of a self-ignited battery. Empty, frozen at -20°C and with a layer of frost around it, I could rather imagine that any kind of defect occurs earlier, even on the circuit boards. But maybe the battery experts know better.

Lifepo are generally considered harmless. However, they should not be frozen. Or rather, especially not charged!

I think Snowy36 meant the fire hazard with that, and does not want the source in the house (basement)

Yes, that's how it is ... I'm only referring to the E-bike battery stories that one has heard ... whether it's realistic I don't know but I then sleep more peacefully

Something like this does happen, albeit extremely rarely.
Storing no fire loads near the storage can never hurt.

For e-bike batteries (where it is not quite as rare for various reasons) there are fireproof boxes or cabinets to charge them in.