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Hi @jeppes ,
This is only supposition on my part but perhaps the battery management system in the tablet needs to detect that there is a battery present (perhaps by detecting a current flow out of the battery and into the load) or detecting that there is a preset minimum battery voltage level before it turns on the charging voltage.
Here is a link that may be of some interest.
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The battery when reattached has a native voltage of 3.42 where it should be 3.7 . When the charger is attached or another external battery, the voltage remains the same. I realize the native battery is bad, but I would expect that the voltage would flux a little when external power is supplied. Just trying to verify its the battery that is bad and not just run down due to bad charger or circuit
Hi @jeppes ,
What is the o/c (unattached) voltage of the battery?
When it is attached it has a load on it which may drop the terminal voltage.
I agree that the charge voltage should be in the region of 3.7 V -4.2V depending on state of charge of the battery
I assume that you have measured the voltage output from the charger?
3.42 unattached. Zero voltage from the battery attachment point (charger) with the battery removed.
Hi @jeppes ,
Assuming that the battery cut off voltage is approx 3.0V then 3.42 represents approx 40% discharged or 60% charged (if my maths is correct).
As your battery (looking at the ifixit battery removal guide) has only 2 wires then the BMS must be relying on the battery voltage to know when to start and stop charging, rather than also having a 3rd sense wire (like some) that also incorporates usually batt temp into the charge parameters.
Does the tablet give any indication regarding the state of charge of the battery, with and without the charger connected?
If you have checked that the wall charger's unattached output is 5V then perhaps you may have to try replacing the battery first .
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