This is incorrect; the cathode only breaks down during a fire or something catostrauphic. Li ion develops higher internal resistance due to SEI buildup, which

This is incorrect; the cathode only breaks down during a fire or something catostrauphic. Li ion develops higher internal resistance due to SEI buildup, which is less plastic and causes voltage sag as ions migrate. However this effect is cubic (iirc, cant look it up on the throne) so at low draw its heavily reduced. What is low draw depends very heavily on the chemistry, but at <1 C most batteries are only a couple percent less efficient. Every other energy storage method including hydraulic is far less efficient.