It appears the N900 is expecting a normal batteries capacity.

By that I mean, I have been using the Mugen for about 16 hours now and N900 still reports 100% full.

So I am guessing it is like the battery is starting at like 200% and may be currently 140% or so according to the N900's calibration.

Odd, Linux on laptops can handle different capacity batteries. Maybe some software updating is needed for this to work better...