Eli5 how one battery charge another until the first is dead?

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I tend to think of electricity like water, like it flows to the object with lower charge(lower water level). But how can I charge my phone off a battery bank until the bank is dead, and the phone doesn’t start charging the battery bank? How do the devices force electricity beyond some “equilibrium” that would occur in the analogy of two tanks of water with different levels are connected then level out to the same water level? Hope that makes sense. Thanks!

In: 10

Unless your phone has a feature to power out on USB/Lightning the primary thing that port looks for is power in and data out.

If the power source no longer pushes current to the device it will cease asking the power source for a charge, and that’s the end of it.

Now if the phone has a mode where you could power out it would most likely be something you set, and not automatically done once the brick is discharged.

If you had just 2 batteries, it could behave like you described… (Assuming they have same internal resistance)

The trick is bunch of fancy electronic…

Lithium batteries usually have 3.7V. usb has 5V by default and 9,12 or more with fast charging…

This separates the two batteries and makes it work

> analogy of two tanks of water with different levels are connected then level out to the same water level?

The phone and power bank batteries aren’t connected with each other through a wire but through an active circuitry acts as a “water pump”.