This may be slightly off the topic

Just spotted this one over dx http://www.dealextreme.com/details.dx/sku.37216. What's interesting is the capacity 4800mah. Not to mention it was around $5(kinda cheap).

It would be great If we can modify this to make portable charger for mobile phones especially N900 by converting the output cable to micro usb and increase the output voltage to 5.5V (according to proporta usb turbocharger 3400 spec).

Quickly googling, the xbox 360 controller takes two AA cells. That pack on DX is "nimh", and the dimensions are approximately that of two AA cells wrapped in plastic case (well, 4mm extra thickness). What the manufacturer probably has done is put two 2400mAh AA cells inside and called it 4800mAh, but we're not that easy to fool.

Two 2400mAh AA cells are 5.76 Watthours. A BL-5J is 4.88 WattHours. On top of that you'd have to run a boost converter to bring the voltage up from 2.4 to 4.2 or 5V, which probably loses about 30%, so then you're down to about 4Wh, or about 80% of the original BL-5J's energy...

Thank you for the explanation =)

I have now two original Nokia BL-5J 1230 mAh batteries connected parallel (2460 mAh?) inside N900, under Mugen cover.

It was not difficult, but it is not easy either. Took me ~5 hours to make everything. One has to be very careful not to shortcut (+) and (-) poles when doing this and getting the cables (soldered) to the right places may be difficult.

1) I disassembled the 1st BL-5J (look at the pic on the previous page of this thread)
First carefully take out the tape, so you can reattach it later.
The whole battery case under the tape is (+) pole and the (-)-pole is in the middle of the battery. The battery was almost empty (3.68V) , just in case....

2) Soldered a blue (-) cable (has to tolerate 1A) to the middle "pin" under the circuit board.

3) Soldered red cable to the plus connector, yet not destroying the female pin connector.

4) Made two holes to the edge-plastic, so the cables can come out but the cover still can be screwed back to the battery, and yet the battery fits inside N900 battery hole.

5) Assembled the 1st battery back together, the two screws and the original "tape"-cover.

6) Charged both battery 1 and battery 2 to full. Both were 4.18V.
Now it was safe to connect them parallel because both had the same voltage and hopefully potential.

7) Soldered blue cable to (-)-pin and red cable to (+)-pin of the 2nd battery. The 2nd battery lies on top of the first one rotated 180 degrees.

8) Made the parallel connected batteries as a one package by taping them together tightly. One has to make sure there won't be shortcuts even when one drops the phone, back cover and the battery-pack flies apart from the phone.

9) Additionally, I disassembled the Mugen back cover to make two holes in it, where one can store extra microSD-cards. Glued it back together.

I estimate, I can have several (4 - 6) extra microSD-cards inside the two holes now. Also, maybe this microSD-card-USB2-adapter will fit inside, which would be useful to transfer quickly lots of files between any PC and N900. If I would be satisfied to have lens cover always "open", even more space would be usable and I could fit this tiny Bluetooth2-USB2-dongle inside also.

(I used to have microSD-USB-adapter, Bluetooth2-USB2-dongle and extra microSD-card all inside the old Mugen cover, but that system was stolen last summer. But the new Mugen cover can be downgraded back to that if one wants. Then one just have to tape the white patch and the magnet to the phone itself to make camera and microSD-card mounting work.)


10) Put the battery pack to the N900, closed back cover, booted the phone and started the test how many hours it will take the consume the battery pack empty (to 3.6V).

Pics:

good work zimon.

it's not the best soldering you have done but as long as the '-' pol has good isolation from the battery since the hole battery, now that you have removed the tape, is '+'.

i'm glad that my guide can help you make a cheap BIG battery.

---- ps. battery will be empty at 3.3V not 3.6V, belive me that has been tested fully -----

----------- side note ------------
more batterys are recieved, but am a little short on time the next days so test will not be done before the weekend.

Yep. That is the most difficult part of that original BL-5J battery, to get the cable to (-) pole and isolate it from all the places where would be (+). That I had to double- triple-check.

I maybe used little too thick cables, but it was what I had and the others I was too afraid to be too thin if N900 tries to charge with 900 mAh. Yes, the soldering could be cleaner and better.

I plan to keep N900 in a Lipo-safety-back for the next night and for the next recharge, just in case.

I cannot recommend anyone to do the same hack.

I think that having that extra cable and connector coming from inside N900 could be easier and safer to make, but it would void the warranty.

my first mod used the same thickness cable as you are using and i have stress tested it to 5A (5000mA) continous and 10A@10minuts

and again 3.3V is empty not 3.6V

I have been thinking about checking the capacity of the big mugen battery since my homemade battery is tested to more capacity then the big mugen battery.
And it would be a nice compareson on the list of battery's.

So if anybody has a mugen battery and want to sell it for cheap or donate it.
Im a 'bit' cheap, hence making my own battery.... but of cource spending some $ making this thread.
And no way am i spending 100$ on a 8.8Wh battery, my battery for my electro ciao cost 280$ and it has 510Wh.....

send me a pm if you have a mugen battery laying on the shelf

Please don't post in the thread since im trying to keep it clean
i think it is nice not going thru 30 pages trying to find anwsers.
i will be adding more info soon on page #1 just to get most questions anwserd for you out there without having to go thru all the pages.

One thing I wonder about the yesterday's double-battery system.
I connected the blue cable to (-) pole of the battery 1 after the circuit board and not before it, like with battery 2.

Now, if there is a shortcut in the 2nd battery, the protective circuity of the 1st battery is disabled and it shortcuts also battery 1.

I didn't find a place where the cable could be attached so the circuity would be in middle of it and the battery itself. How about with those other batteries you have tested?
I reread (Nth time) your first post and looked the pictures, but I am not sure how you have the 2nd battery connected. At least the 1st battery you seem to have connected same way as I have now, skipping over the battery's own (safety) circuity board directly to the poles of the battery1.

I regret I didn't take more macro photos of the Nokia BL-5J battery when I had it open. I have a good photo from front, but should have taken one from the side also to show where the cables really are connected.

Do I see some scorching on one of the battery cells? It's worth keeping in mind that Li-Ion self-ignites at pretty low temperature, 130C or something like that.