My Fossil PDA Upgrades
Upgrading the battery and sound on the Fossil/Abacus Wrist PDA
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1. Introduction
2. Projected battery lifes
3. The battery modification
4. Before and after comparison
5. Upgrading the sound

* I am being called a terrorist, please help! *

1. Introduction

I like my "Palm powered" Fossil Wrist PDA.  The short battery life was my main annoyance for using this wearable computer.  Originally in April of 2005 I thought of using external NiMH batteries by powering the unit through the mini USB/power connector.  It seemed too bulky so I gave up for a while.

Near the end of 2005 my Fossil was only lasting 1-2 days with almost no use, which was annoying as hell.  This time I looked for low cost battery to replace the Lithium battery built into the unit.  I discovered a plastic encased Lithum-polymer battery that fit nicely under the unit, adding about 1/4 inch to the height.  At 550 mAH it has about 3 times the rated capacity of the original Fossil battery.

This modification should work with all similar models of Fossil and "Abacus by Fossil" Wrist PDA with Palm OS.  This includes the Fossil FX2008, FX2009, Fossil Abacus AU5005, AU5006, AU5007, AU5008 and similar.

2. Projected battery life

Here is a table to show the expected battery life if the batteries worked as rated.  Actual life depends on how much you do each activity on the table.

One real life observation is that both my original Fossil, and my newer Fossil Abacus, never lasted as long as battery ratings suggest!  I believe that up to half the battery life may be killed at the start. This is because if you store the PDA it drains the battery to near death.  In addition deep cycles can also shorten the battery life.

I plan to keep the new 3x battery lasting longer using tips to "prolong lithium battery life", from a Google search:

Theoretical Battery life based on battery ratings:
The current measurements were on my unit.  Variations between units may give different results.  Also remember that this table is based on typical brand new batteries, freshly made.  You might only see 2/3 the capacity in a "new" battery when received.  Your body heat while wearing the wrist PDA and air temperature may also affect battery life.
Activity Average
Run time old
180mAH battery
Run time new
550mAH battery
Standby display off 0.6 ma 300 hr (12.5 days) 900 hr (37.5 days)
Standby in watch mode 1.6 ma 112 hr (4.7 days) 336 hr (14 days)
Main menu screen 6.0 ma 30 hr (1.25 days) 90 hr (3.75 days)
Reading a memo 6.0 ma 30 hr (1.25 days) 90 hr (3.75 days)
Welcome program, page 1 15 ma 12 hr 36 hr (1.5 days)
Enter memo w/"keyboard"* 30 ma 6 hr 18 hr
Backlight operation 37 ma 4.8 hr 14.6 hr
Enter memo w/"tracing"* 40 ma 4.5 hr 13.5 hr

* note- The measurements for entering memos was made at a fast pace for both the keyboard screen ( / then ABC from Jot) and handwriting recognition (Jot).  If in input mode but not entering then the current is about 7 milliamps.

Warning:  The following modification could damage your unit or start a fire.  The Lithium battery is "live" while being removed or replaced so it is possible to short the leads, short-circuiting the battery!  Someone experienced with electronics could still make a mistake.  If it is attempted then do it in a location where fire and smoke will not be harmful.
(Only you can prevent wrist PDA fires...)

3. The battery modification

The battery and connector that I used came from, an electronics distributor.  Here are links on for the actual battery and connector:
· Battery - Varta 3.7V 550 mAh, #66590711099
· Connector - Bourns Modular Contacts 4 pos. SMD male, # 70AAJ-4-M0

Parts before modification
(large view)

a. Measuring and drilling holes:  The first step was to measure a position for the connector on the backplate. The connector was put on the lower part of the watch so that the positive and negative leads would line up with the internal positive and negative.  (I did not want the wires crossing inside the unit, room is tight as it is.

Instead of drilling out a complete rectangular hole, the long sides were drilled out then the middle - like a sideways letter H.  This was done so the the uncut tabs formed by the "H" could be bent back to help hold the connector on the sides.  Holes were also drilled on the speaker edge to help let the sound out more (it is the area with the green plastic in the photo).  A few holes were also drilled along the sides for battery attachment.

b. Installing the connector:  The connector was placed in the hole made for it, and the tabs tightened to where it
just held.  Positive and negative wires are soldered to the connector.  The connector is put flush with the backplate - the contacts stick out further for battery contact. Then the connector was epoxied into position.  The wires are also expoxied slightly away from the connector in order to prevent stress on the solder connection.  (The connector was actually made to be soldiered to a circuit board, not wires.)

A layer of green plastic wrap was glued over the holes drilled for the sound.  It is to keep dirt out.

c. Removing the old battery and attaching the new:  To remove the old battery the negative lead then the positive were heated and pulled from the board.

Warning:  Connecting the battery in the following step puts the voltage on the connecting wires.  They must be prevented from shorting out, or it could damage the battery possibly starting a fire.

Contact cement was placed on the back cover and the battery, then they were carefully lined up on the connector leads.  Epoxy was then used along the edges of the battery and back plate to create a stronger attachment.  One advantage of attaching the battery this way is that  there are no wires to short out if the battery gets knocked off the back cover.

Connector added & old battery removed
(large view)

Notice that the unused contacts on the lower edge of the battery can be used to measure the battery voltage.

d. Soldering the battery wires to the board:  Without letting the wires touch, they are soldered to the circuit board as shown in the following photo.  To be safe I put electrical tape over the connector. Once the battery wires are connected, they can be folded into the case as the back cover is closed.

New battery connected to the unit
(large view)

4. Before and after comparison

I am happy that I did this modification even if it looks odd.  It is nice not having to worry about charging the Fossil every few days!  Here is a picture of my unmodified Fossil Abacus, the Fossil with the battery on the back, and my old OnHand wrist computer:

Fossil Abacus, Fossil with external battery, and OnHand wearable PDA.

Here is a log of the battery meter and voltage on the exposed battery connector.  I was using the unit about 15 minutes a day with the time displayed constantly while in standby mode.  All other setting were as out of the box:
Run Time
Battery meter Battery Voltage
4.16 v
2.4 days
3.92 v
4.0 days
3.80 v
6.9 days
3.70 v
7.7 days
3.61 v
7.9 days
auto off
3.55 v
8.5 days
before charging
3.16 v


Next see Upgrading the sound - After doing the battery upgrade the sound was even weaker, so a better piezo speaker was necessary.  The new piezoelectric element was installed on the back of the new battery pack.

For political interest, see Senator Mike DeWine's mental illness problem.

© Copyright 2016 - Michael Lake - Make copies for personal use only.