Thinkpads Forum

I'm attempting the unthinkable here... (No pun intended. ) I've gone and split open the battery of my 770x, with the intent of swapping the cells with new ones.

Now before you guys have a heart attack, I'd like to stress that it's a completely dead battery, and I've only removed the outer shell thus far. Before I attempted moving further, I figured I'd hit up the forum to see if anyone else has experience rebuilding these, instead of learning everything on-the-fly.

So, now for the questions... (I'll include pics later today...)

First, are there any "gotchas" that I should be aware of with this particular battery? (FRU 02K7019)

Second, it would appear that the flat-flex cables have tabs that were spot-welded to the ends of each cell. Would it be safe to pry these tabs off and solder them to the new cells, or are the tabs themselves soldered to the flat-flex cables? It's kind of difficult to tell without pulling it apart further.

Third, are these one of those "smart" batteries that requires being recalibrated/reprogrammed to work properly?

Any input would be greatly appreciated, and I'll be sure to document the whole process as a guide for anyone else crazy enough to attempt this in the future.

I successfully rebuilt the battery for my 365XD a while back using basic NiMH Energizer AA cells.

I soldered them together in series in the same pattern the original cells were spot welded together by lightly scuffing the tops of each battery with the tip of a screwdriver to give the solder something to adhere to. I didn't reuse any of the existing stuff from the old cells except for the + and - to the controller, obviously. There was also what appeared to be a thermal sensor which I hot glued between a couple of the inner cells. It doesn't hold a charge for the full 2 hrs the factory battery was supposed to last for, and Windows doesn't report the capacity properly until it's about to die, but I do get about 45-60 minutes out of one full charge.

I didn't take any photos of how I wired the cells together, but I did take a couple of the innards before I closed it up.

http://i60.photobucket.com/albums/h30/t ... 3ed526.jpg
http://i60.photobucket.com/albums/h30/t ... 3910af.jpg

Word of warning: Conventional wisdom says: Don't try soldering lithium ion batteries together. They are more volatile then NiMh and can explode. Even so, applying too much heat to a NiMh battery can render it useless. Cells which already have a solder tab on them are spot welded to the surfaces; they probably cannot be easily removed and then re-used (unless you have the equipment to spot weld and not solder them).

My understanding is that some (most?) "smart" battery controllers have a safety circuit that will disable itself if the cells are dead or disconnected; i.e., a keep alive function. I also believe that there's a way to reset or jump start it but don't have details about the process. Google is your friend in this case.

Absolutely.

When I soldered the NiMH batteries, I applied a small amount of flux to the scored surface of the terminal and stuck a section of tinned wire to the tip of the battery to minimize heat transfer to the cell.

I know that other forum members have replaced cells in 701C batteries with generic AA rechargeable cells. These are however still NiMh and not Li-Ion cells. I haven't read any stories about any users rebuilding Li-Ion batteries, though. Probably because of the danger related to heating them up, and also the charging controller in some batteries that apparently stops working if the cells are too dead, or are disconnected from it. I don't know if the 770 battery has one.

I have a dead battery for my 770Z, so I plan to just open it up and remove the cells to avoid damaging the charging circuit in the laptop. The 770Z is used so rarely that it's not worth the hassle to buy / rebuild and maintain a battery for it. With enough Thinkpads and working batteries around, it's actually a considerable task to keep the unused batteries properly stored and do an annual check on the state of all of them..

Awesome photos and information theterminator93.
I forever thought batteries looked odd shapes, didn't know that the rechargable batteries can be used for laptops...
I am going to have a field day soon, hopefully I won't lose any fingers.

I've been Googling like mad for days now, but I've yet to stumble across anyone who documented rebuilding this specific battery that I have. So I've already made the plunge. Here's what I've been able to gather, based on my own observations.

This specific battery (FRU 02K7019) has nine 18650 cells, each three wired in series as banks. There's also a temp sensor that's directly attached to the logic board, and a fuse that goes in-line across one of the three cell banks. It's all held together with a thick flat-flex harness, which has bare metal contacts where the cells were spot welded to. In other words, not user serviceable... (No surprise there! )

So, after trying to pry the old cells away from the flat-flex, I decided salvaging the harness was a lost cause. (The contacts and traces kept ripping.) So I'm now making my own out of 14 gauge solid core wire. It won't fit as neatly back into the case, but it'll work. The new cells I've purchased have tabs pre-welded to them, so soldering won't be as dangerous as the alternative, but I'm still a bit nervous about overheating the cells. At least I have a variable temp solder station, which I can't stress enough as being very important to one's personal safety with this project.

Also, when I was removing the logic board from the flat-flex, something shorted and released the infamous blue smoke. It looks to have been two of the flat-flex traces shorting together, since the cells that were connected still held a residual charge, but something in the back of my mind keeps telling me that I fried the logic board. I won't know for sure until I finish wiring the new cells in.

Wish me luck.

Usually nothing ever good comes from releasing the "magic smoke" from inside electronic components. It's what makes those things work in the first place!

So did your project pan out? It occurs to me that flat Li-Po batteries with integrated protection circuits and leads already attached might be a nice alternative to 18650s.

Omineca wrote:So did your project pan out? It occurs to me that flat Li-Po batteries with integrated protection circuits and leads already attached might be a nice alternative to 18650s.

It truly depends on the form factor of they battery you're rebuilding. The Li-Po cells have the benefit of being flatter/stack-able, but they don't have the same longevity that the 18650s have.

As for the project... I've written it off as a lost cause. Most likely, I fried the logic board when I shorted the battery. Ended up buying a refurbished battery from Impact Computers for $70, which works great. I'll get about two hours runtime out of it.