Regarding longer life for LiI - nothing that I know of helps. It's a general rule that rechargeable batteries will last for more partial cycles than full cycles, and that applies to LiI batteries too; don't worry about running the battery flat, just top it up when you feel like it. The main problem with LiI is that it naturally ages quite rapidly no matter what you do with it; some LiI packs last better than others, and not leaving your iPod to bake on your dashboard in summer will help a bit, but you shouldn't expect any iPod pack to be good for much after three years, even if it's never been used at all. Death in two years is perfectly possible; common, even. That's just the price you pay for the excellent energy density of LiI - and it's also why I've got a Luddite affection for NiMH, and even NiCd.
The LiI battery in my iBook seems to last about 12 months. After two years one can either leave the iPod in its cradle and buy a new one for portability, or pay to have the battery swapped.