One needs to specify if this means "cheaper than a new construction fossil fuel plant" or "cheaper than operating an existing fossil fuel plant". Whether a CO2 tax is involved should also be specified. Things will really take off when existing plants can no longer compete (particularly in places like the US where overall demand is growing slowly, if at all). Of course, this will depress the price of the fuel (natural gas is in the doldrums in the US) which will delay things.
Gas is very good for those consistent other times. Batteries are not. Batteries are better for the excess demand during those off times. they offset the backup peaker gas plants as mentioned in the article.
All of which to say the batteries can eat away at the margins of gas plants, but it is incrementally less cost effective to replace each one.
If you operate in an environment where you can supply renewables outside of solar time in quantities high enough to not need the gas, the gas plants will become a lot less useful. Hydro power is the king here. If you don’t have that gas is still probably pretty important.
It might get to the point where a lot of these gas plants are less profitable because they expected to be more relevant and will not be able to justify their fixed costs. But shutting down those plants is probably more expensive to society than just subsidizing them to stay open.
So it’s complicated. The energy and battery side of the inflation reduction act has been HUGE though. Society doesn’t really get how much of an important investment the Biden admin has done here
[1] https://ourworldindata.org/grapher/solar-pv-prices