" They are in use, very small scale now, huge growth is expected as battery tech is dropping in price continuously large percentage every year."
They are not in production yet and they are not improving or dropping in costs at that great of a rate.
Battery/Storage technology has been the problem for around the last 50 years. The limits on them are based on chemistry.
The real issue with batteries replacing peaking plants is a real simple one. A peaking plant can provide peaking for as long as you have fuel. Using Solar or Wind a storm can cause a "peaking" issue lasting days not hours and batteries are practical for those kinds of peaks.
Not to mention that if you are really interesting in reducing CO2 it really is not the peaking plants you want to replace but the coal fired baseload plants.
If you have a cheap enough source of power you could use that power to create methanol or NH4 for storage and use that for fuel cells. The energy density would be much higher than you can get from batteries and pipelines are more efficient than power lines for transporting energy. The problem is that the conversion is less efficient than a battery.
After dealing with decades of battery tech promises it is hard to not sneer at any "replace x with batteries" comment.