J720 Battery Rebuild

I am considering rebuilding my J720 battery pack with higher mAH lithium ion cells. I have come across this website, translated from Japanese on the method to do so:

http://babelfish.altavista.com/babelfish/urltrurl?lp=ja_en&trurl=http%3a%2f%2fwww1.linkclub.or.jp%2f%7ekenfuji%2fjornada.htm#%E3%83%88%E3%83%83%E3%83%97

Has anyone actually attempted to do this job? And if so, how difficult is it? It appears to me the trickiest part is slicing the case open with the utility knife and trying not to rip the copper tape and pierce the old batteries? Any ideas on how to accomplish the task easily and successfully would be greatly appreciated.

Larry

It's easy.

You don't need to slice the case in half. Just hold the battery in both hands, one hand firmly around each end, and twist. On mine it split neatly along the seam, perfect for glueing back together.

Also, you can buy brand new high capacity 18650 cells online for quite cheap.

Edited by Jax184 2007-10-06 4:57 PM

I have found some higher capacity cells, for example 2600 mAh.

Would they work? http://www.megabatteries.com/item_details.asp?id=14348&cat_id=51

And on a different note: would the NEC 900C use the same type of batteries?

Cool! Are you trying to upgrade the standard battery pack or the 24 hour battery pack? If only the standard battery pack is there room to extend the 24 hour battery pack?

I am trying to increase the capacity of the somewhat dead standard pack.

If the twisting method does not work a friend of mine rebuilt a battery pack by putting a piece of a razor blade in a soldering gun and carefully and quickly sliced the pack open.

Since the new batteries are the same physical size as the old ones, any pack can be rebuilt to a higher capacity by using new modern cells.

Hmmmm what kind of gain do you think you can get? 10%? 20%

Well, the original cells (for the 900c) are 2200 mAh. The pack I have is quite old, so it has maybe half the capacity: 1100 mAh. If I use 2600 mAH cells, that should more than double my current capacity... ( of course it is only 20% more than the capacity of a new pack - that is why if I had a new pack, I would not consider rebuilding...)

I did rebuilding batteries for j720 month ago but experiences weren't too good
plastic pack wont open only with twisting I had to use knife
next thing I found that batteries were solded with "point technology" (and not classic soldering as we are going to do) so they fit perfectly to metal ends there(and it's quite hard to separate them - I used knife) and If we do "normal soldering" the battery sizes may increase so we won't be able to put them back into the case

when I actually did soldering I the iron haven't connected with metal ends (and I was doing it for about minute) so I kept trying until I find out that my battery voltage went from 3,7V-0,8V and it's useless now (but I kept them into fridge for couple of hours)

only thing I can recommend you is not soldering batteries but only putting them into pack. Connection will be good and it works - I use this for about month and no problem yet

The stock batteries arn't soldered, but welded together. You're supposed to buy batteries with solder tabs welded onto them and then solder to the tabs. And you must work quickly, applying as little heat as possible to keep the batteries from being damaged. If you try and fail to solder it, let it cool back down before trying again.

So....any luck on the rebuild?

wow, CE Geek.

Another option for cheap per/battery replacement using batteries WITH TABS for easier soldering is to get one pack of 9 produced by Dell. See here:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=180182007226&ssPageName=STRK:MEWA:IT&ih=008 I bought a pack and replaced my dying pack that would only last 30 min. New pack lasts 4 hrs on my Dell. Out of curiosity I opened the old expired pack to see the 9 18650 Li-ion bats with tabs, so I assume the new one is similar, but higher capacity each. I haven't tried to upgrade a bat for my J728, but this would seem to be one approach for $4.30 each (if you don't mind having 9). The 9-pack is rated at 80Whr. Try at your own risk, of course.

Edited by Hal 2007-11-24 2:38 PM