It's the app. man. ...the application manager.
I do not suggest as a newmo (new maemo member) (TM-patent pending) you mess with apt-get.
Not yet anyway.
Anything you need to install uninstall is available in your application manager.
I suggest configuring your catalogues...
disabling all of them and then connect via interwebz to maemo-repos.com
and at the bottom installing and enabling all the available repos for the n900... (extras dev and extras testing are needed only if you know what you are doing and know what you need....so installing them and then disabling them ...until needed...is suggested...)
as far as your batt. issue goes.
Do the breakdown .
Sane approach.
The most affordable, least invasive, least time consuming method 1st.

1- get a new battery. In fact ...get a few new batteries...backup batteries never hurt.

if the new batt displays the same problems...(your description is reflective of a battery that has had it...not an internal device problem...although nothing can ever be ruled out...nor should be ruled out...but let us hope at this point it is your battery...)
then...it is good news bad news

2- bad news...it is an internal device or battery drainage issue...which needs puzzling out...whether that means logged outputs of where the drain is coming from...or worse...some disassembly required (I would hope not..) ...
good news ...it isn't your batteries! yay!
https://www.youtube.com/watch?v=waRq6ZR7BNE
Hope I made that 2nd scenario sound better than it could end up...

Anyway ...
get new batts first...
THEN take things from there...