Fields are plainly a source of free energy, in that e.g., gravity can cause arbitrary blue shifting in photons, and arbitrary acceleration in masses. You can fuss about Potential Energy, but it’s nonsense, especially in the case of a photon, that literally gains Kinetic Energy that was not there before through blue shifting. The more sensible theory of Potential Energy, is that when it is present in a system, it is actually Kinetic Energy that causes no macroscopic motion, and instead causes only small scale motions that must on average “net out” to nothing at the macroscopic level.
Biological life plainly makes use of fields, beyond the obvious of our nervous system, and instead it is a fundamental part of the storage and use of energy in even bacteria, where small scale differences in charges drive molecular machines that, e.g., allow for the production of ATP:
As a consequence, if it’s possible to extract more energy through fields than is consumed through e.g., combustion, then life itself should have figured out how to do this by now, since there is to our knowledge, no laboratory that’s been around for longer than life itself. The general idea being that because it would be advantageous to extract more energy from a field than is consumed in accessing the field, and because the Earth is so large and diverse, and old, it should have occurred by now. This should be measurable, but it would likely require careful, comprehensive, and invasive measurement of all energy consumed by and produced in an organism.
Note that this does not imply perpetual energy, and instead implies that a small bang (from e.g., combustion) is then followed by a bigger bang (from e.g., an electrostatic field), causing the entire process to have a positive yield. This second production of energy might not be translatable back into e.g., chemical energy, and so no infinite loop is necessarily produced by such a process. That said, if it actually turns out that some life generates more energy than it consumes, then it is obviously worthy of study, since human beings might able to adapt these processes into energy producing systems, that would by definition be more efficient than e.g., combustion alone. The general mechanical intuition being that you use chemical energy, or mechanical energy, to access the free energy of some field, likely magnetic, or electrostatic, but anything is possible, what works is what matters.