So at one point or another my phone battery decided to go all end-of-life on me by inflating like a pillow. Oops!
This presented a problem since I rely on my phone to carry two-factor TOTP secrets, and I kind of needed to export them since I didn’t have a recent backup (for unrelated reasons).
The Google Nexus 4 has the unfortunate property that it requires battery power to turn on, even if the micro-USB connection can provide enough current to run the entire phone. So we needed to make the phone think there was a battery present, even if one wasn’t.
I disassembled my phone and carefully removed the (glued-in!!!) inflated LiPo battery. The battery connector is of a form factor that DigiKey doesn’t carry (I looked!), so I had to scavenge the existing connector. I did this by cutting the battery cable with wire cutters, then carefully soldering wire to exposed metal contacts where the connector is attached to the cable:
(I didn’t worry about the T pin. On a normal battery, this connects to ground across a thermistor, apparently 10K nominally, but I don’t have any thermistors on hand and didn’t want to play any unnecessary guessing games.)
This was good enough to connect the phone to a benchtop power supply set to 3.7 V, which convinced the phone that there was a battery connected with something like 40% charge.
This setup strains the definition of “mobile” in “mobile phone” and is possibly
the worst idea ever, but worked well enough for me to exfiltrate the data I
(Originally posted on my How To Make Almost Anything webpage.)
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