Here the phone is being powered from a 12V lab bench supply, via a 99p buck converter module set to 3.7V, connected using a pair of micro test clips to the battery terminals.
As you can see, all four processor cores are running their allocated BOINC WU's. (Ok I admit, it didnt work first time - I had to remember to set the project to run when on battery!)
What is harder to see is the battery level indicator, which shows 17%, and the screensaver view which has the legend "connect your charger"
Ok, so, clearly the phone cannot tell the batteries level of charge. Since the voltage is correct, and slight alterations of the supply up to and including the charging voltage, dont change this, it follows that the other two terminals of the battery - BSI and BTemp, need to be looked at. Its likely that the issue here lies with BSI, which tells the phone what capacity battery it has installed. With no signal, of course the phone cant accurately judge the remaining charge level.
I suspect that this signal is a simple resistor built into the battery, so it remains for me to see if I can establish the value required to fool the phone into thinking it has a 100% charged battery attached.
I can measure 2300ohm between ground and one of the terminals. But nothing measured to the other. Adding a 2k2 resistor between this terminal and ground on the phone didnt change the charge indication, so my suspicion now is that this value is the BTemp thermistor. That should be easy to check - i'll simply warm the battery up and measure it again!
UPDATE - Well, heating the battery made no difference to the resistance. However, I can now explain this. Ive since discovered, and proved to be the case by peeling off the label, that the pin im measuring the resistance to is actually one of the connections (the other being Vbatt) for an NFC antenna hidden under the battery label!
So im still none the wiser how to make the phone think its got a full battery.
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