Unless you have the means of time travel...
As the thread title states...
"Finding N900 batteries in 2016"
may be rather difficult.

Purchasing off the web is dicey ...
hit or miss...
I usually found it to be a miss...

However...
there are a number of decent ones for sale on ebay...
Just must be canny..
caveat emptor and all..
Some are in very good condition ...others are bold faced lies...
check the sellers feedback from customers to be sure..
That was the best way to trust the veracity of the seller and the n900 or n8x0 batteries they were selling...

All told I think of the 20 - 30 batteries I have bought from ebay for my n900's and n8x0's ...3 had poor battery life in them...
the rest were excellent.

Umm, was this supposed to be an answer to my post? If so, then I'm amazed that you managed to do a post that long, without actually answering to anything I asked. In fact, looks like you didn't even read my post.

So, I'm not looking for batteries, nor the year 2016. I have my batteries already, and I'm asking for help to use them properly. Just used this thread, which has quite related discussion already. I could also have done a new topic, but I'd rather use the old ones.

If you were not answering to me, then I'm deeply sorry (otherwise not).

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.

Those batteries I bought have the exact same look with the original one (with that Nokia hologram stamp etc), and they were in sealed, quite original looking packages. So I really am quite sure that they are unused. But of course they may be very old anyway. But do you think that only the storing for that loong could have affected the capacity that much? If they have been manufactured, like, in 2009.

I have seen many batteries of different devices to wear out. Usually it doesn't affect to batteries' maximum capacity (or at least those devices don't tell me so), but they are still able to charge up to 100%. They just get empty faster and faster.

That's why I am asking. Because for me the way these batteries act is new. So I'm wondering that:

- Is the N900 so smart that in can properly calculate the decreased capacity of those old batteries?

OR

- Is the N900 so stupid that it fails to calculate the batteries capacity? Is there any way to help it in doing this properly?

I think the second option could be more correct, because, like I said, those decreased capacity batteries last roughly as long than the not-so-decreased one. So I'd say that the problem is not in the batteries but in the way the device reads them.

Last thing: You spoke about rejuvenating the batteries. How could this be done? I have done some rejuvenating for car batteries, by feeding some constant 14V current to battery before connectng it to a smart charger... Should I do something similar with around 4V of current?

Just googling for "lithium ion battery shelf-life" gives a lot of depressing results; seems that generic internet wizdom gives just about 2 to 3 years of life to a LiIon battery regardless of is it used or not.

That means your 2009'ish batteries went obsolete around 6 years ago.

MOST definitely and most especially will nokia batts lose their charge if stored and not used.
Even if they are in new unopened packages.

The best way to store li-ion batts is to charge them up to exactly 60% and then put them in a cold / cool storage...at a (the exact temp eludes me for the moment)
ONLY then can it be guaranteed that you will not suffer max charge degradation from the batts sitting idle.
even then..your batts will suffer some loss ..but it will be minuscule.
remember li-ion isn't magic...it is still based on the principles of a chemical reaction to produce an electrical stored charge...and the chemicals in question can and do degrade over time, use / misuse and environmental conditions..
essentially and basically the chemicals are separated by a "barrier" between the two chemicals...and when "used" the chemicals are given the allowance to interact...thus creating the electrical reaction...to add to the issue ...the "barrier" separating the two chemicals can degrade as well...

albeit ..it is an improvement over old archaic batteries...

The only way we can be free of the scourge of battery degradation...
Is alternative energy sources...
say...
to leap technologically to running all our devices off of potato generated electricity...


I wish I could say that the issue lies within the device reading the battery..
But since the issue spans further than simply the n900 and maemo5 os line...and actually encompasses many devices and os's..
I believe the issue is chronic in the battery giving up the proper information to the device.

As far as battery rejuv goes...
I have bought many rejuv'd nokia batts from a supplier here in Canada...they are cheap ...they have a 98% charge max ...they perform for years and perform well ...and they are significantly cheaper than brand new original batts.
I suggest you hunt down a proper professional who does such work...
I lastly suggest you do not attempt batt rejuv without some serious training first by someone who does it professionally..

Of course I am writing all this purely guessing at your possible reply ...not that I have read anything you wrote...

actually ...
if we can just whittle it down 109 pounds.....
then we are "a go" ...for the potatophone....
https://www.popularmechanics.com/sci...power-a-phone/

1. Yes I have CSSU testing installed. Do you mean that there is battery optimizations included, or do I need to do something else? I used the phone like 1hour before installing CSSU so can't really tell if there is improvements or not.

2. But mobile network sucks even more battery than wifi, doesn't it? I have tried to optimize, having only 2G constantly on for Pidgin messenger. At home it switches to wifi. Email syncs once per 1 or 2 hours and calendar (via NuevaSync) synchronizes 2 times per day. Someone might go with even fewer synchronizations, but this is what I feel necessary. Besides I have only one desktop with weather and calendar widgets. I'm sure that there would be some more optimization to do, but my main problem at the moment is crappy batteries.

To be honest, I mostly skip your posts due to their rather "stream of consciousnessy" style... But now I'm forced to read them because you are actually answering to my questions. Thank you for your help!

"stream of conciousnessy" style?

hahahaha

If only gestures could be adequately conveyed in text....

I read through your problems; I found no mention for recalibrate the battery. Maybe that could help...