Yeah... the swollen battery... had to do they same task on my harmony 900 (almost the same as one) and was sweating while opening it. Fortunately http://www.harmonyremoterepair.com/ have good how-to's, so I didn't break anything. If you wan't to use your one again, that I'd suggest to buy another one cheaply (perhaps partly defective) at ebay kleinanzeigen (flooded with harmony ones), thus having also spare parts.

OT:
is it somehow possible to subscribe an email notification for this thread upon new replies or so? I know, that I will not often look around here, but would like not to lose track about news hm :/