I just received a battery for my FZ20 that I ordered from Amazon.com - $27.54 & free shipping.
This battery is made by Lenmar (model DLP002) and has a3 year warranty - 7.2 volt / 680mAh
Their web site http://www.lenmar.com
shows it as compatable with the following items.
Maxell #DC3784; Panasonic # CGA-S002; Panasonic # CGA-S002A
Panasonic FZ1;FZ2;FZ3;FZ10;FZ15 & FZ20.