The rechargeable battery has deteriorated.
The supplied rechargeable battery can be charged about 1,000 times (this depends on the environment where the IC recorder is used). If the length of time that the IC recorder can be used approximates only half of the normal time, even after the rechargeable battery is fully charged, replace the battery with a new one (not supplied) (ICD-UX533/UX533F/UX534F only).