The ML150LR/LRS will indicate that the battery needs to be recharged by rapidly dimming the light output (or dimming followed by light shutting off). If the flashlight is used infrequently, the battery should be recharged a minimum of every three months (regardless if no dimming is observed). Additionally, If the light is going to be in storage or not used for three months or more, the battery should be charged and then removed from the light and stored in a safe place.