A bit of background: my girlfriend's smartphone lately has picked up the habit of turning off while the battery is still at about 35%-40%, or so the system says. For anyone around here who is not knee deep in the Android world there's a thing called battery calibration, the system may sometimes report a wrong reading if it is not properly calibrated. There are 'fixes' for this but I am quite sure this whole story is nonsense.
I think the battery is faulty because I once had the device in my hands when it turned off: some strange artifacts appeared on the screen and shortly after it died. I think such artifacts are due to an extremely low voltage, infact I popped the battery out and measured some 3V without load, and that seems quite low to me since that's a regular Lithium-Ion battery.
Before buying a new one, since this is some six months old, I want to test this one to actually prove it's faulty. I was thinking of fully charging it in the smartphone, then connecting it to a load drawing some constant current (a resistor), while monitoring the voltage. Even if this setup is correct or auspicable there still are some questions that come to mind:
- how much current can I safely continuosly draw from it? I was thinking of 100mA but maybe I can go a little higher to make the whole process faster
- how often should I check the voltage? should I expect it to drop suddendly when the battery is nearly empty?
- how low should the discharged voltage be? I know I can search this but a (very) quick search did not answer this so I'm just putting it here because it makes perfect sense.
What I expect is to see a somewhat normal discharge cycle but for a sudden voltage drop when the battery should not be fully depleted.
Bonus: my girlfriend used to fully discharge her phone, as in "damn the battery's dead flat again". This did not happen often enough to bother me (apart unreacheableness) but I'm guessing it played a role in all this.