J720 Battery Rebuild

if that's really 80Whr, the cells seem to be 2400-2500 mAh each, not bad

Wow! Maybe you could custom make a battery pack with all nine for your jornada...really cookin hpc! Might double as a coffee warmer

Edited by pengyou 2007-11-24 8:03 PM

Sorry for digging up this old thread. I guess it is still and probably even more relevant to the current users.
I have bought a 690 after acquiring a 728 for the purpose to rebuild the old 690's bat into a new longlasting one.
So far I think I have done 90% of the job. Opening the battery is not as hard as i think, perhaps because this is not my first time fiddling with such dangerous stuff. Got two new 18650s with 2500mAh each.
But ... the new cells won't charge.
The charging circuit and the board are absolutely fine, i'm sure. I put in the old cells back and it charges again. So the problem must be something about the new cells.
There are a few things i dun understand.
I boot into the diagnostics mode and run the power tests. The old normal cells read 8.7x V, which is expected. But the new cells read 10.xx V! My multimeter read the new cells at 3.7~3.8V. (Aren't all 18650 are about 3.7 V?). So they seem not to be dead cells. The thing is they just refuse charging. Why?
Is it becuase the machine has not get used to the new cells, or because the charging chip is just picky about about brands?
My new cells are not branded. Should I get good brands like Sony and Sanyo, though they are more expansive?
Any help is much appreciated. Thanks!

Got another two Sanyo 2500mAh cells. They seem to have no much charge left when i bought them. This time first I made my J728 eat up all the charge of its original 1950mAh battery. Then I swap in the rebuilt battery. And they WORKED!!
At last my J728 can really go all day long with intensive use.

Anyone else has done this too?

Now I begin to suspect whether the two scenarios have to do with the amount of charge left in the new 18650s. The first pair seemed to get full charge beforehand and the J728 failed to recognize them; the second pair (Sanyo) did not have much left and the J728 can feed them up just like the normal batteries. Am I hallucinated?

I have taken dozens of pics during my experiment and will put them up on my (new) site soon.



Edited by MrSB 2010-02-03 6:33 PM

I've put up my notes here: http://sites.google.com/site/10getgadget01/first-week-part-ii
Tell me if anything goes wrong.

Nice demonstation! one question is how did you connect the terminals to the battery?

As shown in the pictures, I just clip the battery terminals (the "metal flaps" ) on each end of the metal wiring instead of (de)soldering because:

• I want to minimize the damage to the wiring


• I am not very skillful in soldering


• I am lazy

Fortunately the circuit board doesn't need resets, which requires professional tools I can't dream about being able to use.

Google Sites suck (no comment, no direct export, no offline saving)! Will export it to somewhere.

Edited by MrSB 2010-02-06 12:02 AM

Nice. I avoid soldering at first too, so that I don't have to desolder if it doesn't work. But I've had bad luck with re-celling thus far - only one rebuilt battery successfully taking and holding a charge. (Haven't had to rebuild my Jornada batteries yet, though.)

BTW, the negative terminal on a battery is called an anode, not a cathode. (Cathode only refers to the positive terminal.) It's the reverse in the case of electron flow circuits.

Haha ... what will a battery with two pos and no neg look like? The next gen maybe??
Thanks for the correction. Didn't check carefully. I changed the jargons to "poles" to things less technical and more noob-friendly.

Just spotted Samsung 3000mAh for 3 bucks each. Looks like I will be tempted to upgrade my batt again Orz ..

Where????

Just search "ultrafire 3000" on ebay.

Hello!
I have a question: is there a controller inside of Jornada battery like in notebooks that we should reset (with special soft and hardware) after re-celling the battery with fresh cells? I want to repack my J720 battery so i have to know) Also, what is the problem with "noname" cells?

Simply excellent tutorial. Many thanks.
BTW, I used a very similar rebuilding process on a Libretto mini-laptop a couple of years ago. Seems the connections don't need to be soldered to work OK, I just jammed the batteries back in the case with the connections loosely between the cells. Seems to work fine.

Arrrgh....at one time or another, most of us will just jam batteries in and pray they make contact and don't come loose. And for a temporary testing measure, I guess that is okay.

But at the very least, even if you don't want to spot weld or solder the contacts...consider using conductive glue. It works well and will easily handle the current needed for a handheld. And it holds pretty good too. It only costs a couple of bucks on eBay and has a lot of use in fixing these things or repairing a broken or loose wire or pcboard component.





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