Battery calibration on FP5

Help Fairphone 5
1

Hello,
today I was using the FP5 to navigate to work, and the battery plummeted from around 45% to 2% within the span of ~20-25 minutes.
So I took to calibrate the battery. Most guides for this say to let the phone die on its own, and then recharge it while it’s still off, letting it sit at 100% for a while.
When it finally died after being on 1% for 5 hours of use I plugged it into a fast charger, and it started up on its own. This seems to be reproducible behavior, so I imagine this is expected.
I turned it off manually and let it charge while off. The phone started displaying the battery percentage as a fullscreen graphic.
However it stopped charging at exactly 80%, and the charger reported 0.0W of outgoing power.
I just turned it on and it seems to charge further now, drawing around 2-3W (the charger can provide up to 250W via PD/PPS). At this rate, the last 20% will take around 3 hours to fill if the estimation on the phone can be believed.

Which brings me to the question:
What is the actual procedure for calibrating the battery on the FP5?
Should I have turned it off? Do I let it trickle-charge to 100% or am I already done?

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The FP5 is not special in terms of battery calibration. Having said that I’m surprised to read the phone turned on when you plugged in the charger. For me it turns on to a charging animation which it switches off after a few minutes or so and which can be re-enabled by pressing the power button shortly. Turning on the phone only works via long-pressing the power button.
When it is turned off it doesn’t take any of the charging settings made in Android into account. So it charges fast, it charges past any 80% limit, so basically everything that you need for going to full charge.

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Thanks @theodord , please let us know if the percentage indication is now more reliable for you.

As I recently reported here Battery issue FP3 - #32 by Thoense , FP support told me that with recent phones, calibration isn’t necessary but doesn’t hurt either. But I wasn’t very satisfied with their short answer, so I’m curious about your experience.