For a rechargeable battery the fraction of the electrical charge stored during charging that is recoverable during discharge.
This is sometimes referred to as Ampere-hour Efficiency.
The coulometric efficiency is always larger than the energy efficiency.
|Nickel Metal Hydride||0.65-0.85|
Carl Johan Rydh, Bjorn A. Sanden, "Energy analysis of batteries in photovoltaic systems. Part I: Performance and energy requirements", Energy Conversion and Management 46 (2005) 1957-1979