My Nokia N810 has a BP-4L battery with 1500 mAh.The new Nokia N900 will get the BL-5J with only 1320 mAh.
That is 180 mAh less in a successor.
Strange because the N900 has now things like:

-Integrated FM transmitter
-5 megapixel camera with dual led flash
-Call and data features like 3G and HSDPA.

And much more that the N810 did not have , so the N900 will need more power but gets less.
The N900's 1320 mAh battery has 12% (180mAh) less then the N810's 1500 mAh battery.

But there is one thing more to tell about the battery of the n900 , it is only a Li-Ion battery against the much better Li-Polymer of the N810.
When compared to a lithium-ion battery, a Li-poly has a greater life cycle , and lower weight and greatly increased run times.

Nokia gives the N900 not only less battery-power , from 1500mAh to "only" 1320 mAh but also a worse battery-technologie from Li-Polymer to Li-Ion.

I have a feeling they did think about this when designing the device

I think there's suppose to be talk at the Summit about powersaving on the OMAP-platform or something like that, might give a hint about how the battery is going to last you through out a day of use.

EDIT: Link: http://wiki.maemo.org/Maemo_Summit_2...wer_management

Yea but i heard Maemo efficiency of the power management software allow it to run as good a 1500mAh.

You sure about that life cycle ? Regular Li-ion used to be superior in that regard, Li-po advantages being light and custom shaped.

Li-ion have about 1000 charging cyrcles (do i say it right?), while li-po have 500

Li-poly's tend to catch fire or explode when overcharged or physically damaged. Check youtube for all kind of crazy people puncturing them for fun.

There's confusion here. Where can I find a reference to those claims about major differences between li-poly and li-ion? As far as I know, they are for all practical purposes very similar. And li-ion is absolutely as dangerous as li-poly when punctured.

The major difference is really that li-polymer batteries are soft (if delivered without an extra, external hard case) and can thus be shaped to some extent. I replaced the li-ion battery in my Palm with a larger capacity li-poly, as the latter could be shaped a little it was possible to put in a battery with 40% larger capacity. And yeah, it's about 40% larger by volume too.

Well, you could just get a li-ion with 40% more volume and have it have 40% more power as well.

No, a li-ion cannot be shaped like dough. That's the whole point: A li-ion would not be able to fit in the same space (if you've looked inside a Palm with a slider you would know).

ed: typo

Even wikipedia mentions LiPoly internal resistance issues over time, and has some interesting numbers on LiIon aging in general..