I have just dug out my wireless R120 which I bought and have never used. In the box there were two power supplies. One is clearly for the receiver which is clearly labelled 12 volts. The other is a 9 volt supply which fits the R120. The rechargeable battery in the unit is a 4.8 volt NiCd package. The first thing I did was to very carefully open the R120 and replace the CR2032 button cell. To open the case, carefully release the two clips that hold the aerial and power connector and pull them free. Remove the six screws and very, very carefully separate the shells. Then even more carefully separate the circuit boards, noting the way the pins register. In mine the radio frequency board was held in with two zip-ties which I cut to get access the button cell. Consider replacing the zip-ties. Check that the 4.8 volt NiCd is not leaking electrolyte. If you disconnect it, note that the red wire is furthest away from the PCB. The connector socket is not polarised. Reassemble carefully, making sure that the pin connectors are fully seated and the circuit board is located on the small white pillars on the screw holes. Charge for 12 hours according to the Strand leaflet which is visible on the web. Mine has just started to charge and I will let you know how I get on. Regards, Alan.