[Q] Battery % WITHOUT an APP - is it possible?

Dear team XDA,

I have just got a curly question from a client, and looking to the brain trust for an answer.

Can you tell the % of a battery just through how much current resistance/flow it's drawing from a charger?

Use case: I plug my phone into a charger that is designed to measure how much current the battery is drawing and how much resistance there is to pushing more juice in. Can I theoretically know how full the battery is by external measures without installing and app or knowing the mAh size of the battery.

My initial thought was yes, much like how a trickle charger knows when the battery is full. But the client challenged me and asked what if the phone hardware isn't giving you direct access to the battery, or genuine feedback from the battery.

Any help is appreciated, the more I thin about it the less certain I get.

p.s. This isn't my first post, but it is a new account so just seems that way

Renate NST said:

So you want to make a public charging station that knows when somebody is done charging?
That's somewhat easier.

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Hi sorry for the late reply, for some reason I am not getting notifications.

Yes I want to make a public charging station, but I was really hoping to have % of charge. Letting them know when it's finished should be pretty straight forward.

If there is any conceivable way to do % without an App would be great, we are happy to develop bespoke hardware to facilitate.

We have been using an ADAM data acquisition module to monitor AC current into the charger and it's pretty flatline, so not looking good so far: