Replacement Battery

Summary

How to use an off-the-shelf 1Ah Li-Polymer Battery from Sparkfun with bits from a Treo 650 battery to power the Treo 650. The new battery is one-half to one-third (depending on your original battery) the capacity. However, if you're like me and your country no longer supports 2G mobile phones, then you won't be using the power-hungry phone part anyway.

Introduction

This year (2021) my last Treo battery finally started puffing up and needed to be thrown out. It almost made it to the recycling before I realised it was my last opportunity to try to extend the life of my Treo a little more. I would really miss my Sudoku app! Not to mention being able to use Astromist with my telescope.

I tried to source a replacement battery, but that disappeared into the postal system - or the seller never actually had one. Official (or even unofficial) versions of these batteries must be getting a bit old, and probably not in very good condition. I hoped there was some other option.

I tried just powering the phone from USB, and while that worked, the phone insisted on shutting down immediately because there was no battery. I then tried connecting power directly to the battery terminals inside the phone, but that had the same result.

At this point I decided the best course of action was to re-use some 1000mAh Li-Polymer batteries I had purchased for another project. I tried one in the battery compartment of the phone and it fit almost perfectly.

To understand more about the Treo650s power system I opened up the phone following the iFixit Palm Treo 650 Repair instructions. I found that it contained a MAX1587A Power Management IC and a MAX1874 1-Cell Li+ Charger. The datasheet for this chip indicated it was designed for 3.7V LiPo cells and a maximum charge current of 1A. That confirmed the new battery would be compatible and wouldn't be over-charged - a 1AHr capacity Li battery should not be charged using more than 1A (or a 850mAh battery charged using more than 850mA, etc).

The next job was to understand more about the Treo 650 battery itself.

The Battery

My battery was marked "Type: 157-10014-00" and "DC050626 SAMSUNG SDI-DGO". I started my unwrapping the battery - peeling off the gray stick-on film and some black sticky tape around the sides.

That revealed the battery to be two cells in parallel. One of the cells was marked "800mAh" which meant the whole battery was 1600mAh. Note that the red side is actually the negative terminal of the battery, and that the silver side - indeed the entire silver casing of the battery is the positive terminal.

Removing the last bit of black tape - be careful here - you're going to want to keep the bit of plastic it is stuck to intact - revealed a small circuit board. Cutting the metal strips allowed the circuit board to be removed, along with another bit of plastic that should be kept.

The Treo 650 battery can now be disposed of - properly!

The back of the PCB reveals a DS2762 Battery Monitor and associated components.

I de-soldered the metal strips and replaced them with black and red wires.

Then I reassembled the plastic bits. If you re-assemble them with the inside plastic bit around the 'wrong way', then when the PCB and outside plastic bit go on, the end of the bottom plastic bit will butt up against the inside of the Treo battery compartment and the PCB battery contacts will be perfectly aligned with the Treo battery contacts.

Next, I trimmed the red and black wires and soldered them to a JST Battery Connector from Sparkfun. Then I was able to position the PCB so it was making contact with the Treo battery terminals and insert the Li-Polymer cell to press them together. Last step was to connect the battery - the Treo immediately turned on.

The new cell is only half the thickness of the original cell, but that allows room for the battery connectors to fit - in fact they prevent the new battery from moving in the compartment and keep the PCB in contact with the terminals.