The number of CPU credits that an instance has accumulated, reported at 5-minute intervals.
You can use this metric to determine how long a DB instance can burst beyond its baseline performance level at a given rate.
When an instance is running, credits in the CPUCreditBalance don't expire. When the instance stops, the CPUCreditBalance does not persist, and all accrued credits are lost.

This metric applies only to db.t2.small and db.t2.medium instances for Aurora MySQL, and to db.t3 instances for Aurora PostgreSQL.