I haven't read the 505 threads in quite some time but today logged on
and saw this post. For anyone who is searching these posts for z505
battery solutions and is handy with a soldering iron and is
*attentive* to the very real dangers involved, I have a great solution
for you.

If you are like me, you have collected over the years a stack of dead
BPZ51's and BPZ52's. They are filled with Panasonic CGP345010 prism
cells. Pansonic upgraded this cell years later to the CGA103450A
taking you from 1400mah to 1950 mah/cell. These are hard to find and
industrial supply representatives are reluctant to ship small
quantities to the average person. I found one on the Panasonic
website that shipped me four for $58 (the BPZ52 needs 12). I could
not find a refiller that would refill with these batteries as they are
outside of design.

I will leave it up to you to figure out how to crack the cases of the
BPZ's without tearing them up. The batteries are glued to the insides
of the cases. The Z51 is fairly easy, the Z52 not so easy. The
covering to the new batteries is very thin so you need to protect all
surfaces after soldering to prevent arcing lest you get the magic
flame. Also, I never owned the battery pack in between the wafer that
shipped with the Z505 and the big brick so I can't speak to this. I
suppose it had 8 cells.

After several deep discharge cycles on my reassembled BPZ51, I am able
to get 1:40 of full out time on the z505hs, no power management (all
devices in control panel set to never sleep), wifi card in, streaming
tunes off the net. A new Sony replacement, as you know, gets about an
hour. My z505r now gets over 3 hours with the same battery and power
management on.

As an aside, the most common (and cheap) lithium cell on the market is
the 18650. Don't try to put these in your BPZ52 case (they won't fit
in a BPZ51). The charging characteristics are so significantly
different that it won't work and it is apparently not good for the
charging circuit. I whacked two battery controllers trying. It would
be cool if someone could post their experience removing and
reprogramming the EEPROM on the controller using the tools and
software available on the net. I didn't feel that aggressive.

I hope this helps someone. God Bless my Z505's. They won't die.