strat (FZ10 gallery) (Yahoo! FZ10 group, 26 April 2004)...
Not an authoritative answer but I recently read that lithium and NiMHs will both lose charge over time. According to a laptop battery site, these batteries keep a charge for two to three months, slowly losing their charge however.
I found the site and include the info here. Keep in mind that this applies to the much larger, laptop batteries but the advice seems good (except for the uncertain remark. You'd think they'd know by now).
Lithium Ion Batteries (Li-Ion) {such as the Panasonic uses}
1 to 2 months -- Battery should still have minimal charge to operate the computer
6 to 12 months -- Battery can still be charged
12 months or more -- Uncertain
Batteries may be damaged if stored for prolonged periods with a closed circuit. The environmental temperature also affects the storage life of any battery. Cool environments are best, and are assumed for the above estimates. All storage times are based on storage starting with the battery fully charged.
For example, schools that may not use their {laptop} computers during the summer should fully charge the batteries, remove them from the computers, and store them in a cool location for the duration of the summer.
{Picture below taken by Stratis}
