There's no substitute for Cubic Inches 
"2014" options for replacing your battery with something bigger.
I own the P211(120GB) PM, though I'm sure that the 666? (60GB)
may use the same battery.
I thought it might be helpful to share this for those who are interested.
This is not a Step-by-Step guide
I ASSUME that persons who are attempting this have a rudimentary understanding of electronics, possess tools,
skills and knowledge required to dissassemble, determine best fitment method and assemble your device without damage!!
This information is correct at the time of posting.
I have been able to locate, what appears to be the Datasheet for the battery, or at least one that is so close as f..k is to swearing
Here =>
http://www.ciblenergie.fr/pdf/LPD723048%201100mAh.pdf
Otherwise search for "LPD 723048 1100mAh".. anyway dimensions for the battery are as follows:
Length: 48 ±1 mm (not including tab length)
Width: 30 ±0.5 mm
Thickness: 7.2 ±0.3 mm
I had actually already ordered the 1400mAh(left) and 1800mAh(right) based on measurments I made from the original battery.
The 1800mAh being the desired fitment, with the 1400mAh being the backup if I wasn't happy with how the larger would fit.
The original Battery shown here.
As you can see, the 1800mAh is a very snug fit that requires arranging the battery in such a way as to minimise potential damage to either the PM or battery when closed.
When positioning the battery, it has to clear the DIL connector on the left(green) while at the same time adjust so that there is enough clearance so the DIL header doesn't damage
the battery when assembled, clear the Hard Drive Locating Stays??(Middle Red Dots) and squeeze in between the two 'Feet' molds(Left Red Dots) as shown with the blue arrows.
Even then, it is still a tight fit
Effort required will vary depending on the battery size tolerances.
The 1400mAh, while still a slight squeeze, will allow the PM to go together easier being 2mm thinner.
Both batteries can be found with this seller on ebay
http://www.ebay.com.au/sch/hunk_lee/m.html
Admittedly I didn't look much further since I was happy with my choices.
The 1800mAh is currently listed on ebay as "103450 3.7V 1.8Ah GPS MP4 Notebook Phone LiPo Battery",
the search "103450 3.7v" (as I write this) results in 3-4 items(worldwide).
Length: 50 ±1.0mm
Width: 34 ±1.0mm
Thickness: 10 ±0.5mm
The 1400mAh is currently listed on ebay as "803448 3.7V 1400MAH Li-Polymer MP4 GPS PDA PSP battery",
the search does not work for some reason as above but the seller is
http://www.ebay.com.au/sch/hunk_lee/m.html then search for "803448"
Length: 48 ±1.0mm
Width: 34 ±1.0mm
Thickness: 8.0 ±0.5mm
