So I mentioned on the
Replacement Batteries thread that I had invested in 8x LG HG2 18650 3000mAh cells.
The batteries arrived this afternoon and I decided to take a crack at doing the cell replacement for my BlueBerry iBook.

1. All lined up, ready to go. These appear to be genuine and do feel "solid". I haven't handled any cheap cells, but my understanding is they often come in substantially lighter, because they are only partially loaded.

2. First up, I've unpacked the existing battery and here I began to remove the first two cells from the circuit. The cells coming out are Panasonic CGR18650HM.

3. Here I've prepared the orientation and marked the new cells where the leads are to be soldered back on.

4. All 8 original cells are safely removed and set aside. To remove the spot welded tabs, I just peeled them back and forth with a pair of pliers until the two spot points on each terminal were released. I was fortunate to not break any of the tabs during the removal process.

5. Here's the bare circuit ready for the new cells to be loaded in.

6. Half way there. The first four cells are soldered onto the circuit's tabs and the blue lead is reattached.

7. Ok, after a lot of swearing, sweating, a few burns on my hands and knees and a couple of scary moments where sparks flew, we have our repacked battery. It looks tidy enough, but the top half of the shell refused to fit back on, so I ultimately just taped it up and peeled the full-length sticker (which has some kind of conductive strip under it) and stuck it bare atop of the cells.
I ended up packing some thin card between each pair of cells to keep the circuit from stepping short. I taped the whole thing up with electrical tape after this and reinstalled.
At one point I thought I could hear the battery cells sizzling and popping, so I threw it into an empty a bucket and raced outside with it, expecting a flare up of smoke, but nothing happened. I picked it up and the cells were perfectly cool, then I realized that the "sizzling" noise was just the original adhesive inside the battery case letting go in slow creaking/popping moments.
Once packed, the battery reads ~14.8v. In the process, I managed to somehow destroy my "el cheapo" multimeter, which is now massively out of whack (And doesn't have an internal calibration pot it seems)
Some notes for future attempts...
As I am learning the ropes with the soldering iron, and this was my first battery attempt, I was really unsure about how to approach things. My solder blobs could have been tidier, but I was careful to only apply very short bursts of heat when soldering on as I didn't want to overheat the new cells. I cranked my little 40w iron up to max to provide the quickest transfer.
In the future, I will certainly want to invest in some flux instead of relying on the flux in the solder. It took me a few attempts until I got into the groove, then while attempting to pack it back in the case, a couple of my cold solder joints let go. So I stepped back, (cursed a bit *ahem*), took a deep breath, then tore it back down to tidy it up and tried again with a more even heat between surfaces. I am confident that the soldering is strong now, but what a steep learning curve!
It was tricky to try balancing the pack of cells while working on it from different angles. I settled for big wads of blutak and book ends while I was trying to refit the cells onto the terminal tabs. An extra pair of hands would have helped immensely. (or maybe a bench vice?)
Also, I really should have used some fine grade sandpaper to score the terminals first. The surfaces are well polished and took a bit of convincing for the fluxed solder to like it.
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The moment of truth and the iBook boots! The battery's capacity is still listed as 3392mAh, which I believe is the same as it was before the new cells, so I imagine the battery's controller needs to be recalibrated by doing a full charge, followed by a full drain. The 3.7v cells by 4 is 14.8v, so the two pairs of 4 cells at 3000mAh, should equate to a capacity of 6000mAh, but maybe all of my "first time fumbling" will have a negative impact on this.
Despite my iBook's "26w" issue, it is charging the battery fine while the iBook is sleeping (or shut down), and is now at 70% charge. I'll wait for it to finish then give it a good run through in "mobile" mode
I will be the first to admit that I had very little clue here and this is a dangerous repair to do. I mostly winged it and it's not pretty, but it does work (so far). I am confident that it is safe enough to use (for myself), but I will be keeping a close eye on it.
The usual disclaimer applies: Don't try this at home folks! Unless you're fearless, stupidly confident, or just gifted with good luck! It IS possible to burn your house down while messing with these cells. The warning of "Do not short circuit" is for reals and not the usual overly-cautious, safe-to-ignore kind of warning you see printed on things.
(I'll post an update to confirm capacity once it's done recalibrating.)