My Polarcell 1500mA/h batteries from cellphone.de when combined into a double battery(supposed to be 3000mA/h) for Mugen back equipped N900 have already dropped down to 2128mA/h after only 30 days, I am pretty disappointed considering the price paid.
I wonder if they went with a new cheaper supplier after getting a good reputation, I wish we still had Scud batteries available, cheap and amazing capacity, lifetime over two years.

Sorry to hear that. Must have changed their manufacturer, or some such, as they were good a while back.

Dam... I've just ordered another one a couple weeks ago !!!

I would try to get some sort of warranty replacement but I think soldering two cells together pretty much voids any hope for replacement.

The standard (on this site) way of soldering the cells is almost guaranteed to destroy the capacity.
If you measured the capacity as soon as you have soldered the cells and then 30 days could there also a chance of damage due to the heat. If not, then my guess is the cells have a combined capacity of 2000mAh from damage. This is what happened to me. Heat solder damage.

Out of four soldered packs only one measures at double of a single paired up.

I now leave the cell protector circuit on the cell. Gently prying off the plastic cover. Gently cut a channel for the wire in the bottom plastic cover, hot melt over the top. The gold contacts get carefully snipped to a nice flat shape and very very easy to solder too.

The top cell needs to be placed a little further rearward for the mugen cover to fit as you still have the protection circuitry but sans plastic cover and with hot melt for protection.

What a beautiful thread, thanks!

@independent, what I did was lifted both of the regulators so the leads were exposed.
I then snipped the leads of the add-on cell at the regulator circuit board.
I slipped shrink tube over the flat leads coming form the add-on cell.
Finally I bent and soldered the leads of the add on cell to the regulator circuit board.
Sometimes I trim plastic to make more room, sometimes I need to remove the bottom plastic strip so the battery does not cause the GSM to become disabled.
This still generally needs some tweaking to get the phone to recognize the battery, just adjusting the angle of the plastic housing for the battery regulator circuit, insert, and try to start.

It could be that my phone is getting old but I do not remember having any of this getting-it-to-work hassle with Scuds and I always got at least 3000mA/h for several years.

Some information.
Today there is 0$ shipping to Poland promotion on Mugen's website.

Is it still needed to install KP47 to measure real capacity? If so, how to get it ?

I've tried on kp53 latest cssu stable but keep getting ./i2cget not found error, even if it is placed there. Perhaps a reboot.

I'm looking at getting a PowerCell. There are 2 on ebay from the same seller. Other that a slight difference in price, 1 states "MPN: Nokia C3-00". The other says "MPN: does not apply". Any ideas what this means, any difference?
Apparently MPN means manufacturer part number.