i think i'll start making 3d-model of the casing today after work. now i'm glad our company buys all electronics from one place. better chances to negotiate more reasonable prices to these small private projects.
It was mentioned here before, but really: the Nokia DC-11 is the solution in terms of hardware. It is explicitly mentioned right on the first pages of the manual, in an advertisement (for this and the bluetooth speakers, to "share your experiences").
this is only a hobby for me. nice to have a project sometimes. specially now when i got moved to another department @ work. it means i can use companys soldering irons, cnc & manual machining tools and other equipment for free at my spare time(and when those aren't used for work) as long i don't do business with things i create.
and this is an idea that is easiest to pull through from all my crazy ideas. (EN1.4404 enforced camera module for any backpack, ESLUT -loudspeakers, and stuff like that aren't so easy to do compared to this)
According to this link: "Most cells are charged to 4.20 volts with a tolerance of +/-0.05V/cell. Charging only to 4.10V reduced the capacity by 10% but provides a longer service life. Newer cell are capable of delivering a good cycle count with a charge to 4.20 volts per cell"
The PCB you mention seems to have a cutoff of 4.35 volts. So it's a protection circuit rather than a charging regulator.
You should use a protection circuit like this one, but you also need a regulator. Again, according to the above link, a good way to charge lithium-ion batteries is:
charge with a constant current (at the cell's rated charging current) until the cell is charged up to its voltage limit, then...
maintain that voltage until the charging current drops to 3% of rated current, then...
switch off the charger, i.e. don't keep trickle-charging
Finally got things moving. I found out that the batteries already have safety circuits. plus I realized that the bundled charger adapter is a miracle maker. http://www.dealextreme.com/details.dx/sku.29208
(NOT ORIGINAL!! AT YOUR OWN RISK!!!)
I can charge n900 only by plugging a battery to the adapter.
Just a spare CA-146C charger adapter, piece of wire plus plug from old nokia charger (big headed), 3x spare batteries and external charger from dealextreme.
then I just soldered the wire into the charger and voila.
Now I can always charge external batteries with any nokia charger, and either use one external battery as spare power/minor loading or switch phone off and switch empty battery into full one.
