hahaha
actually I didn't read your post ..figuring it was yet another person posting in a very old thread.

It would have been better to post under an existing thread dedicated to battery issues and concerns or making your own thread.
and I believe for the edification of others who have similar problems to move your post and subsequent answers to said places where others will be looking for it.

4 points to take into consideration of your situation.

1- if you have cssu and (consequently the) battery optimizations done to your newly acquired n900. You will notice a marked improvement in battery longevity.

2- wifi and BT suck a generous amount of battery ...as well ..having lots of widgets ....

3- your charger ...even though you are trying to be fastidious in making sure you are using the proper devices for charging...it is possible (though not probable) that the charger may be part of the culprit....it depends. I have used official nokia chargers and generic chargers and found that the generic ones can work better than the official nokia chargers...if the nokia charger is faulty.

and lastly 4-
the batteries themselves...
the first you mention ...is in it's later years of age now...seen lots of use ...but has a decent charge left...(the one sitting fully charged at 94%)

the other two ..are not new...at all.. or are poor generic bl5j's ..
it is characteristic of old ones that are ready to die...
that they sit at a lower state fully charged..(ie : your 77% batts)
(....I have in fact a couple batts..1 for the n900 and 2 for the n800 ...the lowest of which sit at 84% (and I thought THAT was low fully charged...for batteries that were heading to their doom...you beat my record) fully charged ...and they act the exact same way as your batteries are... Out of all 30+ of my batteries those 3 show the exact same symptoms you mention....your issue ..with batteries here...is age....if they are rejuvenated...then they can be given a second life...otherwise they are on their way out...and are soon to be only good ...if you are keeping your device plugged in as a stationary unit.)

They will most certainly act fine...and not budge an inch in their displayed charge...until the moment that it plummets and starts warning you of impending shutdown.
This endemic of a battery on it's way out.
It makes them unreliable in daily unplugged usage.

So there are your potential and most likely culprits...

And in my characteristic nonsensical manner...
I still stand by my stance of initially not reading your post
and only succumbed to a peek of it.