Here are a bunch of pics from my battery pack rebuild. It's a 9 cell 18650 pack, with SMBus, fuel gauge, protection, etc. I'll try to go through the process, and mention any gotchas as well. But first of all... let me start by saying I've never rebuilt an 18650 battery pack, and I don't own a battery tab welder. So, I bought batteries with tabs already attached, so I could solder to them (soldering directly to 18650s is hard, and the heat isn't good for the battery). The battery tab welder would have made things quicker and easier though.
The obvious things: safety first... lithium batteries hold a lot of charge and can be dangerous, catch fire, etc. Pay attention to battery polarity, and don't attempt this if you don't know what you're doing.
I chose the HyperPS brand batteries, with tabs attached, which were <$3 each shipped on ebay (these:
www.ebay.com/itm/272359448176 ). They claim guaranteed >2600mAh, but suspicious of unknown brands, I made sure to test them in my BT-C3100 charger/tester before building the battery pack. These actually tested quite well, >2800mAh each. In case you don't know, fake 18650 cells claiming ridiculously large capacity (6000mAh, 9800mAh, etc) are all over the place, and generally they are actually junk (<1000mAh). A real 18650 will generally be around 2000-3000 mAh. The original batteries were MOLI FSPE.70037 (ICR-18650G), which were 2000mAh cells.
GOTCHA: make sure the length of the new cells are close to that of the original cells (~65mm). The original cells are unprotected, so you'll probably want to stick with unprotected cells, as the protection circuit generally adds a little bit of length, and there isn't a lot of extra room.
To open the pack, peel back the short side of the label (or cut it, though if you leave it in one piece, it works well to hold the pack together). Go around the edge of the pack with a knife to crack the small dots of superglue holding the plastic pieces together at the edges. You can also crack the glue by twisting it like you're popping ice cubes out of a tray.
GOTCHA: the pack was assembled in the bottom half (side with the battery contacts), and then some RTV was put on top and closed up. You want to disassemble it in the reverse order. If you pull the pack out of the bottom (like I did), it'll bend the battery contacts and rip the LCD cable (I ended up replacing it with standard 0.05" ribbon). Instead, you should open the pack by prying the top from the batteries. Then, once the top is open, lift the pack straight out of the bottom. Clean out any large globs of RTV from the case so they don't interfere with the fit of the new cells.
Once it's out, desolder the two tabs from the PCB, undo the Kapton tape holding the fuses, and cut the metal strips connecting the fuses to the batteries (leaving as much of the strip as possible, as you'll probably want to reuse it), and remove the PCB and fuses. Once that's removed, you can pop apart the original pack and see how it's connected... it's 3 series packs of 3 batteries in parallel. You'll want to start by assembling your 3 parallel battery packs. If using the solder kind, rotate the tabs so you're soldering away from the center of the battery, so it'll solder easier, and apply less heat to the battery. Make sure the tabs also line up on all packs, so they're easy to connect in series. The battery pack is tight, so try to keep the solder fairly low profile. Once they're all assembled, drop them in for a quick test fit.
Next, you need to add the tabs that go to the PCB. Look at their placement on the original pack, and try to get it as close as possible on the new pack, so the PCB will fit properly. I added Kapton tape between the packs, so all current will flow through the tabs... though that's not very important, as they're connected in series anyway. I then soldered the tabs between packs together and slipped a piece of heatshrink over them and taped them down with Kapton. I then transferred over the tape from the old batteries to the new ones for the boards and fuses, and put a few pieces of Kapton over the pack to keep it held together. I desoldered the red and black wires from the PCB (so the PCB was completely out of the way), and connected the fuse tabs to the tabs on the ends of the pack, and cut off any extra tails. I then put Kapton over the ends, since there wasn't enough room in the pack for the cardboard endcaps that were on the originals.
This gives you batteries fully assembled, with a red and black wire and two tabs sticking up. Then solder the red and black wires to the PCB and press it down over the tabs and solder the tabs. Then carefully drop the entire pack into the bottom of the shell, making sure the battery contacts go straight into the slots. You may need to pry the plastic back a bit on the LCD end to pop the LCD in place. Then with a multimeter, make sure you have around 11V across the points where you soldered the red and black wires.
Finally, temporarily close the lid, slide it into the E7495, and make sure it's functional before permanently closing it up. Once you know it works, I'd put a few dabs of superglue around the plastic shell, pull the label tightly over the shell and seal it up (the label should still be tacky, but will probably need a bit of glue/adhesive for a permanent seal).
The battery fuel gauge will be wrong (mine said 0% when it started, even though it already had a half charge), but after a full charge and discharge, it figured itself out. There's an option to refresh the battery on the E7495 (automatically charges, discharges, and recharges), though it didn't work for me (it never completed because the gauge never showed that it was fully charged).
Anyway, I hope this helps... or convinces you to just spend the $200 on a new one. :-P
Pat
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