Charging and discharging batteries is a chemical reaction, but Li-ion is claimed as an exception. Here, battery scientists talk about energies flowing in and out as part of ion movement between anode and cathode. This claim has merits, but if the scientists were totally right then the battery would live forever, and this is wishful thinking. The experts blame capacity fade on ions getting trapped. For simplicity, we consider aging a corrosion that affects all battery systems.

The charge algorithm for NiMH is similar to NiCd with the exception that NiMH is more complex. The NDV method to measure full charge shows only a faint voltage drop, especially when charging at less than 0.5C. A hot battery or one with mismatched cells works against the already minute voltage drop.