The feature that affects how often a battery needs to be replaced is its lifespan, which determines how long the battery can last before it no longer effectively holds a charge. Capacity affects duration between charges, but not replacement frequency. Other factors like safety and carbon footprint are important but indirectly related. ;
The total charge delivered by the device is 450 C, which corresponds to approximately 2.81 x 10^21 electrons flowing through it in 30 seconds. This is calculated using the relationship between charge, current, and time, along with the charge of a single electron. Therefore, a significant number of electrons pass through the circuit during this time frame.
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