Eli5: How does a power bank charge a device until it dies, wouldn’t equilibrium be reached?

Question

Eli5: How does a power bank charge a device until it dies, wouldn’t equilibrium be reached?

In: 551

Answer 1

An analogy using water is like transferring water from bucket A (initially full) to bucket B (initially empty). Yes, on level ground the water levels would just equalize, but what the circuitry inside a power bank essentially does is to raise bucket A as it empties (Eg someone lifts it as it empties). This way, the water level in bucket A stays constant relative to the ground, even if the water level relative to the bottom of bucket A changes. Accordingly, bucket B continuously fills.

Eventually, you just run out of water in bucket A. Lifting it any higher won’t give you more water. That’s when the power bank runs out of battery.