[NTLK] MessagePad 2100 recell problem

[Gavin Watson]

A while ago, I rebuilt a MessagePad 2100's spare battery pack with  
regular store bought Rayovac cells.  They are the type rated for 1000  
cycles with no memory effect.  I am having a number of problems with  
it, the first of which is that they are too thick to fit inside the  
Newton, forcing me to insert them without the top to make them thick.   
The second problem is that the thermistor wasn't easily salvageable.   
The third problem is that it only works 1% of the time.

The first day I rebuilt it, it would not work.  About 11:30 that  
night, it decided to turn itself on, though the Newton's battery gauge  
behaved erratically, randomly changing the reading.  Every one to five  
minutes, it would shut down by itself until it stopped working at  
about 11:45.  I've spent a few days checking the battery connections  
and everything looks okay after resoldering one wire that broke.  I  
read that it was the thermistor's positive end (it is the really  
fragile one in the bottom right, rear case open and facing you).  I've  
tested power with a multimeter and found that it outputs comparable  
power to the known working battery.  After fixing the above wire, I  
found that the known good battery's life increased from about 20  
minutes to about a half an hour with no backlight.  The other battery  
still does not seem to work.

As far as construction goes, I had to make a few modifications.  The  
biggest one is that I had to replace the thermistor with a small  
strand of copper wire in order to complete the circuit.  Otherwise,  
I've used electrical tape to reinforce pretty much everything except  
the negative terminal in the battery.

As for the battery's behavior, when it is inserted, the Newton says  
"Charging" with a full black bar for about two minutes before finally  
saying "Charged" and displaying a full gray bar.  When I unplug it, it  
dies instantly and the Newton usually says that the battery died,  
though sometimes says that all power was removed.

The battery electrically works, the Newton recognizes that it is  
there, but it will not work for any length of time, except when it  
randomly turns on.  But my non-refurbished battery works fine.  I'm  
really stumped here.  Does anybody have any other ideas?  Thanks in  
advance.