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iPod 5.5g battery voltage reading

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KhronX:
I just took the iPod apart to probe things again.

On pin 1 of the LTC4066 (Out) i'm reading 3.88v, on pin 2 (Bat) about 3.91v, while Rockbox (in System - Debug - View Battery) is reporting 3.6-3.65v.

The battery graph indicator at the top of the screen is (allegedly) almost empty, by the way. If 3.6v is supposed to be close to "empty", that seems like a slightly too conservative value to me; 3.2-3.3v or so would be a bit more... practical, shall we say?

KhronX:
Just to "double-check", i recharged the battery under the stock firmware (ie. booted with the "Hold" switch on), went up as one might expect to 4.15v.

Right now i've booted back into Rockbox, i'm measuring 4.12v on the "Bat" pins of the LTC4066, while Rockbox says the voltage is hovering around 3.85v, give or take.

Changing the battery capacity in the Settings menu doesn't seem to change anything.

dreamlayers:
Can you boot into original firmware and try to see if battery voltage measurements are wrong there? I wonder if there's a hardware problem in your iPod. But if there is a fixed relationship between measured and actual voltage, you could create a custom build which corrects the voltage measurement.

KhronX:
In the original Apple firmware, that battery bar-graph thingie at the top shows something around 60-70% or so (eyeballing it), while i'm measuring about 4.10V. That doesn't sound 100% right to me either.

I'm starting to wonder... In newer li-ion / li-po powered equipment, there's usually a "gas gauge" chip of some sort. Is that somehow implemented in software in this iPod perhaps, or..?  :o

Does Rockbox only use that battery voltage as a source for the battery indication?

saratoga:

--- Quote from: KhronX on April 04, 2018, 05:23:03 AM ---Does Rockbox only use that battery voltage as a source for the battery indication?

--- End quote ---

Yes, but voltage is the only way to assess the state of charge of a lithium ion battery without discharging it completely.  There are no other parameters you can measure in real time.

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