What is the self-discharge rate of alkaline and NiMH batteries?
Alkaline batteries stored at “room temperature” (70 degrees F) self-discharge at a rate of less than two percent per year. However, if they are stored at 85 degrees F they lose about 5% per year, but at 100 degrees F they lose 25% per year. NiMH batteries self-discharge at a much faster rate than alkaline batteries. In fact, at “room temperature” NiMH batteries will self-discharge approximately one percent per day. This is the primary reason behind our recommended two-week check and charge schedule. Because the voltage of an alkaline battery drops at a very predictable rate it’s possible to estimate the amount of capacity left in an alkaline battery based solely on its voltage. (1.5 Volts – fully charged, 1.25 Volts – 50% charged, 1.0 Volts – almost fully discharged). But a NiMH battery stays at about 1.2 Volts until it is nearly completely discharged. This makes it almost impossible to know the amount of capacity left based on its voltage alone. It also leaves you very little warning
