Sounds like your battery is toast. I would try a load test on the battery or buy a new one.
either that or the charging system... but it is very likely to be a bad battery. one or more of the cells could be bad, which make it virtually impossible to charge properly.
i went to work with a buddy doing CAA, and they have this really cool battery/charging system tester. with a few simple tests, it can tell you whether the battery is bad, or the charging system is bad, or if there is a current draw, etc. i'd love to get me something like that, but for $3000 or so, no thanks :lol: