I've been looking at it this afternoon. I have a 7.4V 6600mAh pack which gives about 20 mins life . Getting the case open needs a bit of care; it looks as though it has been welded or very well glued together. I worked carefully along the seam on the back of the back with a Stanley knife and after a bit could see the blue covering of the cells. Same along te side seams - a bit trickier because they have a couple of corners but eventually things freed up enough to move. I was then able to lever the two parts of the shell apart so that they hinged along the front seam that eventually cracked open. Glad i hadn't cut there because there is a circuit board that could have been damaged. The pack comprises 2 sets of 3 18650 Li-Ion batteries. Each set of three is connected in parallel and then the two sets are series connected to give the output voltage (hope that's clear.
A bit of careful adhesive/potting compound scraping released a board mounted ? temperature sensor ? fixed to one of the batteries and then cleared away enough gunge to allow all 6 cells and the pcb to lifted clear of the bottom half of the case. That's as far as I've got and I know I haven't wrecked things completely yet because I've been able to put it all back together and put it pack into the computer and writing this on the power it contains.
There are now two problems.
The first is that the sets of three cells are custom assembled by spot welding onto specially shaped connector plates. Replicating this is not a diy option. It is gong to take careful arrangement of cells and routing of wires to get an equivalent assembly of individual cells back into the case but I think it looks do-able.
The second is that when, without having yet broken any connections, I measure cell voltages with I get 3.9v for one set of three cells and over 4 for the other. It's difficult to interpret such measurements but there seems to be chance that the cells are healthy and that it's the pcb that is faulty in which case a repair is out of reach.
So now is the decision point. Do I disassemble further, buy new cells and try to rebuild. Or do I accept that a new pack from pcbattery.co.uk at ??30 + ??4pp really is the best bet. And I have to admit that I have already bought a new pack. Do you really think I would wreck the broken one without having bought a back-up? The only small drawback is that it had to come from Hong Kong and took a month rather than the hoped-for 15 days to arrive. I think the company is genuine and offers good quality. I hope not to have to put their two-year guarantee to the test. It's just that the post from Hong Kong isn't as fast as you would expect when buying from a .co.uk website.
Any further comments / advice particularly on identifying defective cells would be most welcome.
