# Phone battery replacement with DC power supply

I am looking to use the Alcatel 1 cell phone without battery.

For this purpose, I disassembled the battery and took out the lithium cell. Instead, I connected a DC power supply.

The cell phone turns on perfectly, but after a few hours it shows on the screen that the battery percentage decreases. It continues to decrease with the hours, until it finally turns off.

How could I solve it? At all times the DC power supply remains at 4.4 V.

• Seems you can’t fool it. Give it a battery and power it via the charge port. Aug 13, 2022 at 3:42

The basic problem is that the phone is designed to run off a battery. It has some model of a battery in its software that calculates the remaining battery power in some unknown manner.

What are the possible solutions that come to mind?

1. Reverse engineer and reprogram the phone battery management.

probably way above your abilities and not worth it anyway.

1. Try to fool the battery algorithm by removing the battery management chip from the disassembled battery and feeding your 4.4V directly at the battery terminals of the phone.

This may or may not work, but is the easiest to try.

1. Try to fool the battery algorithm by feeding charging voltage into the charging port.

This will probably work, but requires 2 power sources because most phones cannot run off the charging port input without a battery. If you are lucky and the phone is stupid enough, you may go with a single source fed at both the battery terminals and the charging port.

The phone battery contains a BMS (Battery Management System) chip which, among other things, monitors current passed through to compute battery consumption. It cannot use voltage alone because Lithium rechargeable cells have a fairly flat voltage through most of the discharge cycle. The BMS is reporting the battery level to the phone.

I don't think you can do what you want.

Try this and see if it helps: adb shell dumpsys battery set level 100

Also, 4.4V seems a bit high to me. I usually keep mine in the 3.9 to 4.2V range. Keep messing with the voltage and see if the situation imrpoves. Different devices have different logic to handle charge and respond differently to voltage / current they see. If you have salvaged and reused the BMS off a factory battery, battery reserve estimation is also a fuction of ambient temperature (e.g. may appear to lose charge faster if too cold or too hot).