(In a perfect power priority world, which this ain't) Or you layout a much cheaper battery setup. You don't want your factories slowing down for that, so either you over build your base load power supply to the point some of it sits idle. Why use a battery system in the first place? It's biggest use is to buffer your power grid during peak demand, perhaps all your ILS send off their fleets at once, and suddenly your grid demand spikes an extra 600 MW.
No really, except being used in energy exchangers the accumulator buildings are entirely lack luster.
