We want to keep a Xiaomi Mix smartphone powered on for a very long time (>6 months) with power from the USB cable. This is not recommended by the manufacturer since the battery will be constantly at 95-100% and topped up by the charging which is bad for the LiPo cells. We have already tested leaving the phone plugged in "stock configuration" and seen batteries swelling after about 4 months, which is not good.
I don't need any "battery functionality" since the phones will be plugged in with the USB cable the entire time, so one idea to prevent the swelling is to remove the LiPo cells (and keep the battery protection circuit plugged into the smartphone) and replace them with some equivalent circuitry. My question is what would that equivalent circuitry look like?
The battery I want to "emulate" is a BM3B manufactured by SCUD Electronics. It is a 3.85 V pack with 3.3 mAh.
My initial tries with just a resistor (R = 470 kOhm) and Capacitor (C = 10 uF) in series has not worked. My idea with that circuit was that the phones charging circuit would charge up the capacitor to ~3.85V and then measure that the battery was full, proceed to drain energy from the capacitor, discover that it was draining quickly and proceed to charge it again. But it did not work, the phone powered on for what looks like a microsecond and then dies.
How can I simulate a battery?