Editing Nickel–metal hydride battery (section)

=== Trickle charging ===
The simplest of the safe charging methods is with a fixed low current, with or without a timer. Most manufacturers claim that overcharging is safe at very low currents, below 0.1&nbsp;''C'' (''C''/10) (where ''C'' is the current equivalent to the capacity of the battery divided by one hour).<ref name="duracell_charge">{{cite book | title = Charge Sealed Nickel Metal Hydride Batteries | work = Ni-MH Technical Bulletin | publisher = [[Duracell]] }}</ref> The Panasonic NiMH charging manual warns that overcharging for long enough can damage a battery and suggests limiting the total charging time to 10–20 hours.<ref name="PanasonicChargeMethods" />

Duracell further suggests that a trickle charge at ''C''/300 can be used for batteries that must be kept in a fully charged state.<ref name="duracell_charge" /> Some chargers do this after the charge cycle, to offset natural self-discharge. A similar approach is suggested by Energizer,<ref name="NiMH handbook" /> which indicates that self-catalysis can recombine gas formed at the electrodes for charge rates up to C/10. This leads to cell heating. The company recommends ''C''/30 or ''C''/40 for indefinite applications where long life is important. This is the approach taken in emergency lighting applications, where the design remains essentially the same as in older NiCd units, except for an increase in the trickle-charging resistor value.{{Citation needed|date=June 2015}}

Panasonic's handbook recommends that NiMH batteries on standby be charged by a lower [[duty cycle]] approach, where a pulse of a higher current is used whenever the battery's voltage drops below 1.3&nbsp;V.  This can extend battery life and use less energy.<ref name="PanasonicChargeMethods" />