Thanks very much for your replies. I have now managed to open one of the handsets (whilst supervised by a responsible adult) and I have taken the batteries out of it. They are branded "Highpower". I suspect this may not be an entirely accurate name. Although I have given up on these handsets I have ordered some replacement batteries from Amazon. I am curious to see how well these handsets perform with different batteries in them. I can always make use of the batteries in other devices if things don't work out.
I will report back with the findings of this exciting experiment in due course.
Thanks,
CDA.
You can just use ordinary batteries to test the phone just don't connect to the recharging base