A battery is a chemical product which produces electricity by chemical reactions at its inside. These reactions and its inside materials do deteriorate over time. If you start using it within that period, the battery will operate normally and maintain the specified performance.
In appliances without a charging function, yes. In appliances that do have a charging function, be sure to check whether the function was specifically designed for Ni-MH. If not, it’s best not to use Ni-MH batteries.
Avoid contact with the substance at all times. Place the batteries into a plastic bag before recycling them. Clean out the battery holder with a dry cotton swab. In case of contact, wash your hands thoroughly with soap and water.
The memory effect is an occasional defect, which occurs in Ni-Cd and Ni-MH rechargeable batteries, where the maximum battery voltage decreases even though the original power of the battery remains the same.