In today's society, digital products are becoming increasingly popular, but this has also led to the problem of insufficient battery life. The power bank was born in this context, and for this reason, the power bank industry has developed rapidly. So, how many times can a fully charged power bank charge a phone? Is it simply a matter of dividing the power bank's capacity by the battery's capacity to get the number of times it can be used? While theoretically this is correct, in practice, it's quite incorrect because there are losses during the conversion process. Today, let's explore together how to calculate how many times a power bank can charge a phone, hoping this will be helpful.
Let's explore this issue using iPhone charging as an example! Generally, to improve compatibility with digital products, we consider the output voltage of a power bank to be 5V. The internal lithium battery of the power bank and the lithium battery of the phone have the same voltage: 3.7V. The discharge termination voltage is 2.75V, and the charging limit voltage is 4.2V. However, when both voltages are 3.7V, charging is impossible. Therefore, the power bank must boost the voltage to 5V to charge the phone battery.
The power bank's built-in battery voltage is 3.7V, and its output voltage is 5V. The built-in battery needs to be boosted to 5V via a DC-DC boost circuit before it can charge the phone.
Battery energy = Battery voltage × Battery capacity
= 3.7V × 1120mAh
= 41.44Wh
The built-in battery voltage is 3.7V and the capacity is 11200mAh, so the battery energy is 41.44Wh.
During charging
1. Under extremely high power conditions, without considering any losses, the conversion rate to 5V is 100%.
According to the law of conservation of energy:
Output capacity = Battery voltage × Battery capacity × Conversion rate ÷ Output voltage
= 3.7V × 11200mAh × 100% ÷ 5V
= 8288mAh
Therefore, the battery voltage is 3.7V, the capacity is 11200mAh, and the output voltage is 5V.
With a conversion rate of 100%, the maximum output capacity is 8288mAh.
2. Of course, losses due to the conversion of the boost circuit are unavoidable; a loss of 15% is generally considered excellent. Vision Power's losses are within 10%, meaning a conversion rate of over 90%, a pioneering achievement in the industry.
Calculate the output capacity using the following formula:
Output capacity = Battery voltage × Battery capacity × Conversion rate ÷ Output voltage
= 3.7V × 11200mAh × 90% ÷ 5V
= 7459.2mAh
Therefore, the battery voltage is 3.7V, the capacity is 11200mAh, and the output voltage is 5V.
The conversion rate is 90%, and the maximum output capacity is approximately 7459.2mAh.
Number of times an iPhone can be charged = Maximum output capacity of the power bank ÷ Phone battery capacity
= 7459.2mAh ÷ 1440mAh
= 5.18 times
Therefore, a 11200mAh power bank can charge an iPhone approximately 5.18 times.
