Duracell further suggests that a trickle charge at "C"/300 can be used for batteries that must be kept in a fully charged state. Some chargers do this after the charge cycle, to offset natural self-discharge. A similar approach is suggested by Energizer, 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.