I have a Reedy 5200 60c saddle pack. One of the cells has gone bad. I want to open it up to see if there is any internal damage to the one pack because it hasn't been used much at all. How do I go about opening up the hard case?

I'll save the "it's not safe, don't do it" speech/reply for someone else-

I did this out of curiosity a few times. I used some state of the art equipment, needle nose pliers. Of course, since the halves of the cases are normally glued together, they become scrap after. If the pack has wires protruding from the case itself, start by prying from where the wires exit out by squeezing one of the jaws in and then bend the plastic outward. Once you have a start, keep twisting the plastic, avoiding leverage onto the cells and trying to keep the edge of the jaws at the seam where the halves are glued, the glue will give out fairly easily. If the pack has female bullets, you can start by using a small flathead screwdriver where the hole is for the bullet connector until you can fit a jaw from the pliers in there. Most packs have a small board where the metal tabs from the cells are arranged, and those are usually covered with some thin tape. Of course you should be aware of not shorting them out with foreign metal objects (tools). Also, most packs have enough space at the end where the connections are to not cause any damage to the cells, whereas everywhere else the cells sit pretty flush to the case.
You could start by prying the seam at the connection's end of the pack with a small flathead, then go around the whole thing in an attempt to be able to tape the halves back together, but it's more risky, time consuming, and the case may be too trashed in the end anyway.

Actually, before you open that pandora's box, in what way is one cell damaged? Voltage too low? Or not balancing?

It will not hold a charge. If you try to charge it, it goes up a couple millivolts and then starts dropping back down to 0 while still charging. Or it just doesn't take a charge at all. I talked to the lhs and they said it's okay to charge on a NiMH setting to give it a little voltage (my lipo setting wasn't picking it up) but this still had the same affect.

I mean I can replace it, but I am curious to see if something is broken inside, and whether I can fix it or not because it is not an old pack.

The pack does in fact have bullet connectors, so I'll try prying there. I was worried about damaging the cell by cutting elsewhere around the pack. Thanks

http://www.youtube.com/watch?v=UClcOe8bmAA