Mechanical vs. chemical vs...? Energy Storage?

Question

Which is more efficient, mechanical or chemical storage? An example is a spring vs a battery, and efficiency would be in terms of energy:weight, energy:volume or energy:cost. Just curious.

Answer 1

Agree the spring is likely to hold more charge, longer, than the battery.

Answer 2

A weight on a tower will store energy for a while. I vote mechanical.

Answer 3

A battery can lose charge over time.