Editing Nickel–metal hydride battery (section)

=== Δ''V'' charging method ===
[[File:Charge NiMH.svg|thumb|NiMH charge curve]]

To prevent cell damage, fast chargers must terminate their charge cycle before overcharging occurs. One method is to monitor the change of voltage with time. When the battery is fully charged, the voltage across its terminals drops slightly. The charger can detect this and stop charging. This method is often used with nickel–cadmium cells, which display a large voltage drop at full charge. However, the voltage drop is much less pronounced for NiMH and can be non-existent at low charge rates, which can make the approach unreliable.<ref name="duracell_charge" />

Another option is to monitor the change of voltage with respect to time and stop when this becomes zero, but this risks premature cutoffs.<ref name="duracell_charge" /> With this method, a much higher charging rate can be used than with a trickle charge, up to 1&nbsp;''C''. At this charge rate, Panasonic recommends to terminate charging when the voltage drops 5–10&nbsp;mV per cell from the peak voltage.<ref name="PanasonicChargeMethods" /> Since this method measures the voltage across the battery, a constant-current (rather than a constant-voltage) charging circuit is used.{{citation needed|date=May 2025}}