Hello Amoult.
I'll try to answer you but am myself still a newbe, so ... sorry if i'm mistaken.

1/ As you stated it's not normal, battery life is great on N8xx

2/ I read trough the forums that some softs can drain the battery really fast, especially softwares that are still in beta and available only in non official or garage repositories

3/ Did you install EasyDebian (Qole's amazing work) ? If yes, maybe you put the system in "performance" mode to run it and simply forgot to swich back to "on demand"

4/ Did you install a status bar applet called " advanced power " ? it's very usefull, and gives you an option to change the CPU policy ... maybe it's stuck on "Performance"

5/ I'm not specialist with home applets (I simply never use it) but i would'nt be surprised if one of them is keeping a connection active to check something on internet ... did you try to put the unit in flight mode ? did you try to deactivate all home applets ?

6/ I wouldn't be surprised either if your SSH server is guilty ... maybe it doesn't deactivate properly ? (Never used it, but it sounds logical that it will eat your battery quite fast) try to deactivate or remove it ...