[infogulch]

The efficiency loss compressed air suffers is mostly at the hands of the ideal gas law. Storing energy by pressurizing the container heats up the gas which increases the pressure requiring even more energy to store additional gas. When retrieving energy it depressurizes the container which cools the gas down which reduces the pressure which gives you even less energy. What if they could cancel out?

Say you have two separate pressure vessels where to charge the system you pump air out of one into the other. Well the depressurizing vessel will cool down, but the pressurizing vessel will heat up. If they came to thermal equilibrium with each other their net temperature change would cancel out somewhat. This is great because it would restore the pressure on both sides to have more favorable conditions for energy storage and extraction.

So I wonder if you could design a pressure battery that would exhibit no change in temperature on the exterior throughout the charge/discharge cycle.