One of the main disadvantages of most rechargeable NiMh and NiCd batteries available today, over standard alkaline batteries is the high self discharge rates. If you charge rechargeable batteries to their full capacity and then use them after a month, you will often find that the batteries are drained. These batteries have to be charged again before they can be used.
The self discharge rate depends on the brand and design of the batteries, with some manufacturers advertising a low self discharge rate .