Modifying Android Phone To Run Without a Battery

Intro

I had few use cases where I needed a constantly on Android phone. The issue with keeping any device constantly charging is that their battery will suffer. In case of lithium-ion batteries they have a proclivity to inflate and even catch fire or even explode. So keeping your mobile phone charging all the time is a big no no.

Luckily there is a way to solve that issue by ripping out the battery and adding an external power source instead of the battery, but even this may not be so easy since more and more entry level phones have a built-in a hard to replace battery, so you really have to find a right phone. I tried this mod on several phones LG (with removable battery), Samsung (With removable battery), Nexus 6 (with embedded battery).

The results were:

So this post will cover my journey of hacking a Samsung XCover 4 to run w/out a battery.

The Guide

The schematics are relatively simple. I used a 5V, 2A AC/DC power adapter. You may say ask why I did not reuse the original charger? Well the original charger had 2 issues:

If the phone gets some heavy load e.g. a video game it may start shutting down or the battery level may drop below a 100%, and we don't want that let's just tell the phone the battery is at 100% all the time. The battery % may fall because the charger's voltage begins to fall sharply if high current is required by the device that's why I chose to buy a 5 V, 2 A adapter and not use the original charger.

Now you may ask but won't 5V directly to the battery pins damage the phone? Since li-ion batteries are usually rated @3.7 V, yes 5V directly may damage the phone's electronics inside, so I dropped the voltage using a single component since I wanted for the circuit to be as simple as possible. I just used a high current FUF5408 diode. You should keep in mind that diodes don't drop voltage at a fixed point they also have some Volt-ampere characteristics (i.e. voltage drop across diode based on passing current).

Here is the original schematics (not very clean I know!)

schematics

R_1 = 12k Ω, 0.25 W Resistor
D_1 = FUF5408, High Power Diode

[NFC] -- Not used
[-] -- Negative (-) power rail duh
[S] -- Thermal resistor pin, originaly thermal resistor is built into the battery.
[+] -- (+) 🙄

here is how the module looks like when soldered

sk-module

As you can see module uses 4 pins well actually only 3 of them since the left most pin is used for NFC data. Yes Samsung batteries have NFC antennas glued on the batteries and not build it into the phone, since I did not really need the NFC I did not bother connecting it. Also, as mentioned before thermal resistors are also a part of the battery, that's why we used 12k Ω resistor, because we need to fool the phone into believing that battery temperature is OK.

sk-module2

module back

For the soldered module I used simple breakout board. Fun fact Samsung battery pins are spaced in the good old INLINE manner meaning that the distance between the centers of adjacent pins is equal to 1"/10 = 2.54 mm.

module-wire

If you are attentive enough you probably noticed that the top part of breakout holes are cut in half having a U shape and not plain O hole shape. This was intentional, because I wrapped the contact pins w/ one striped wire from the CAT-5 cable.

product

And here is how finished hack looks like. I simply used hot-glue to keep the module in place also make sure you hot glue the wires as well so that under tension they don't transfer any "wobbliness" to the module itself.

Final Thoughts