Likewise. So far so good with a Craftsman lithium battery for a combo set of which I normally use a drill and circular saw. Previously I used two nicad batteries with the set which survived some extensive boat restoration project. They both finally died, after being resuscitated a few times with high-current jolts to each cell from a 12V battery. Replaced about 3 years ago with the smaller lithium battery sears sells. Haven't seen as intensive of use, but so far I'm impressed. More charge, no under current/voltage issues, and it hasn't diminished noticeably yet like the nicad did. That said, I also try to make sure the battery isn't ever drained fully and probably only seen the equivalent of 100-200 full cycles in that period.
From what I understand lithium cells lifetime is determined by the number of cycles the cell has undergone, not how it is stored or memory effects. Thus they need to be used differently than nicads. I also suspect there are cell quality differences (QA binning at least) but don't have enough experience to fully comment on that. I know from electronics work and using some 1.5KWH lithium batteries for AUV work that swapping lithium cells isn't hard as long as a similar form factor can be found, but prices seem to vary depending on source. And keeping the inside of the cell dry is important...and the resulting fire is hard to put out
