Chargedischarge

Charge–discharge refers to the two fundamental modes of operation of energy storage devices, such as batteries and capacitors. Charging is the process of applying external electrical energy to store energy in the device, while discharging is the release of stored energy as electrical power for use.

In electrochemical storage, charging drives chemical reactions in the opposite direction of discharge, forcing ions and electrons to accumulate in specific electrodes. Discharging converts stored chemical energy back into electrical energy as reactions proceed in the forward direction. The performance of charge–discharge cycles depends on chemistry, temperature, aging, and operating conditions. Key concepts include state of charge (SOC), state of health (SOH), depth of discharge (DOD), and cycle life.

Charging methods commonly used for batteries include constant current (CC), constant voltage (CV), or a combined CC-CV approach. Fast charging can shorten cycle life and increase heat, so management systems adjust voltage, current, and temperature. The discharge rate is described by the C-rate and is tied to available energy and power. Round-trip efficiency reflects losses during both charging and discharging.

Devices vary in behavior: batteries (lithium-ion, lead-acid, NiMH) store significant energy but discharge relatively slowly compared to capacitors, which provide high power over short times with rapid charge–discharge cycles. Battery management systems monitor voltage, current, temperature, SOC, and SOH to maintain safety and longevity.

Safety and environmental aspects include protection against overcharge and over-discharge, thermal management, and end-of-life recycling. Poor charge–discharge practices can lead to overheating, gas formation, or degradation of capacity.