As back-up for my digital camera, I fully charged a set of AA , and carried them in a battery box with no chance of accidental connection. When I needed them some time later, they had completely discharged. Do rechargeable batteries leak their charge over time? If so, why, and how long does it take? For extra back-up, I now carry a set of ordinary alkaline batteries as well.
鈥� Nickel-metal hydride batteries have a high rate of self-discharge 鈥� about 30 per cent per month. This means that every two months their charge diminishes by a factor of 2, and in a year they will discharge to about 1.4 per cent of their full charge 鈥� effectively dead.
Nickel-cadmium batteries are somewhat better, and lithium batteries are much better at only about 2 or 3 per cent discharge per month. In 2005, low self-discharge NiMH batteries were introduced. These are sold as pre-charged or ready-to-use. They are more expensive than old-fashioned NiMH batteries, but can be used in many applications, such as a clock, where normal NiMH batteries would be unsuitable 鈥� though in some of these applications it might be more economical just to use non-rechargeable batteries.
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Eric Kvaalen, La Courneuve, France