Minkoff, I bought replacement cells for my Panasonic from this site:
http://www.all-battery.com/index.asp
They didn't stock an exact replacement, so I bought 3 cells of the correct size and removed the connector off the bad battery pack, soldered the 3 cells together with the connector.
The portable handset is on a Fax Machine, and I didn't want to replace the whole machine.