Well just random apps you know. Beside I dont know which apps does what to the RAM. FYI, I dont have N900 yet. lol. My point is to walk backward and follow the steps you took to find the answer

SInce I don't have a 900 I don't know how helpful this will be but from my 800 I have learned to set the refresh time on the rss reader and anything else that needs to update to at least twice what the default is.

Also I check modest from time to time to see if it choked, which it does often, which can lead to battery drain. And occasionally browserd will duplicate itself and eat battery. I think fennec (firefox) is "browserd" now so that may not be an issue.

So generally I'd suggest checking the update intervals. Also since this is now a phone, if you're in a spot with poor cell reception your battery is going to get drained because the phone is trying to reach the cell tower more frequently (or whatever it does in poor reception conditions). That alone kills the battery on my chinese iPhone knock off in 24 hours even when I've not used the thing.

Its strange that the original OP says it only happens some times. If I didnt know better I would say it was a signal problem and the phone was trying to connect over and over, especially if something was running that required a feed.

Nothing drains the battery on my g1 like being in a bad signal area

I'd agree normally but actually my n900 battery stands up quite well to being in a poor signal area.

My N900 seems to be working fine now, since I recharged yesterady evening. I still have an almost full battery right now after 12 hours.

I tried using the "top" command in xterm window again, this time sorting the processes with the P and M keys (as jaysire suggested, thanks!), but found nothing abnormal, all processes under 5%.

When I had the battery problem yesterday, I had no active data connection, no browser windows open. The device was inidle connection.

I'm wondering if there could be some kind of issue with the N900 wifi receiver being turned on even if the status icon doen't say so? (Could have something to do with the fact that occasionally I disconnect from my wifi router, and if I want to reconnect, the N900 won't see the router until I reboot it). Or maybe sometimes when charging the N900 reports the battery is fully charged but it's not...I really don't know. I will have to wait for it to happen again and investigate further. If it won't happen again so much better.

All I know is that now everything looks good, the battery seems to be performing very well. Yesterday I was shocked to see it get empty in 4.5 hours on and idle device...

I had the same issue when I first received my phone. I was charging it sometimes more than once a day. I started searching online and found this forum. Unfortunately nothing on this thread was very helpful. I started looking at the different settings for my N900 and realized that the GPS had been enabled out of the box. I disabled GPS by going to 'Settings' and then 'location'. This increased the battery charge-life exponentially. I also decided to turn off bluetooth until I actually need to use it. I hope that this is helpful.

I had the same issue. After removing facebook and OM weather, my battery improved greatly. Yesterday at this time (noon) my battery would be about half dead (after disconnecting from the charger around 9AM). Today, after disconnecting from the charger around 7AM, my battery right now is still near full. And I've used the N900 more this morning than I did yesterday morning.

That's the point: the problem appears with a wifi connection, and then stays until a reboot is done.

@marauder: please as you stated above now the device is running quite well with normal battery duration, so can you share your free ram as reported by top command in a shell?

I'm convinced the device has some problem with wifi, during "high battery drain" periods I fell it become quite warm.

quark, the top command in xterm gives the following:
Mem: 194344K used, 51204K free, 0K shrd, 2004Kbuff, 59652K

but I stopped caring about ram usage as sljonson said that:

"The kernel will tend to use most of the memory available as the system runs.The expect stuff will be application code and data pages. The kernel will use the rest for file buffers so it can avoid having to access (abysmally) slow disk (as compared to RAM). The kernel is quite deft at managing RAM. RAM is a very slight battery drain as compared to te CPU running at full speed, or the WIFI or Ceullar radios."

I've read that more than once. N900 will usually use all available RAM.

Battery is still good now. Looks it is going to last the whole day and maybe even a little more...