trouble shooting dectalk express

[cris]

Hi folks,
My dectalk express suddenly stopped working.  When I turn it on it gives the
message that battery is low, and then it starts making weird noise and stops
talking.  It gives this message even when it is connected to external power.
In the past, the message i got was "dectalk express is ready, external power
on."  Could this mean that the battery needs to be replaced, or is it that
the power adapter is no longer working?  Does dectalk express work on
external power alone, without battery?  If the battery is to be replaced,
can I get it replaced in a regular store, or it can only be replaced by
dectalk?
I would appreciate any help.
Cheers,
Cris