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iPod 5.5g battery voltage reading

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KhronX:
So, i have my old (bought used in 2007) 80GB iPod Video, which last year i shoehorned a 256GB mSATA SSD into, as well as a 1000mAh battery.

It all works fine, except for one glaring issue - the battery voltage, at least as far as the firmware is concerned, has an offset of about 0.3V.
Specifically, the firmware thinks the battery voltage is lower than it actually is. I'm measuring for example 4V on pins 4-5 ("BAT") of the LTC4066, while in the Debug section, the value reported hovers around the 3.7V mark.

After booting into the stock Apple firmware, the battery shows as fully charged (measuring 4.18V on the above-mentioned pins 4-5 of the charging chip).
Rebooting into rockbox, with the display off, i'm measuring 4.05V, still close-enough to what should be "fully charged". And yet, Rockbox is only seeing it at 3.76V / 12%.
I'm sure you'll agree, that's not right, and it's highly doubtful it's a hardware issue. unless it's somehow related to the ADC that's doing that particular measurement.

I'm on the latest stable Rockbox, with the added patch from BeyondWind, that fixed an apparently common ATA error with SSD's.

I'd appreciate whatever thoughts and ideas some of you more knowledgeable folks might be able to provide...

KhronX:
Anyone...?   :-\

dreamlayers:
The most easily accessible battery voltage is averaged / smoothed, to reduce the effect of fluctuations such as when spinning up a hard drive.

So, go to System -> Debug -> View battery, and then scroll one screen clockwise so you see the screen with "Pwr status:", "Battery:", "USB pwr:", etc. You should notice that the battery voltage there is changing all the time. That is the real time reading. If that is wrong then you really are encountering a problem.

KhronX:
That is indeed the reading i was comparing with what my multimeter was telling me (in real time).

<edit> If memory serves, i was probing (near) the pin of the LTC4066 chip, where the battery positive terminal goes - i wanted to see if there's any drop between the battery and the chip, thinking it might be reading wrong, but nope.

Rockbox and/or the circuitry (the ADC in the SoC?) in my particular iPod seems to be consistently reading the battery a good 2-300mV lower than it really is.

dreamlayers:
Did you look at the LTC4066 OUT pin? There should be some voltage drop between the BAT pin connected to the battery, and the OUT pin powering the device. The iPod may be measuring the OUT pin. But, they're connected via an "ideal diode" circuit and the drop ought to be less than what you're measuring. LTC4066 datasheet: http://www.analog.com/media/en/technical-documentation/data-sheets/4066fc.pdf

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