The PRAM Battery is a 3 V Lithium button cell soldered onto a small daughter board beneath the speaker and microphone. Be sure to use proper ESD protection when pointing a soldering iron towards the board! Also be careful when using a multimeter. Several circuits of the 180 do not like high test voltages; use a multimeter that is appropriate for use with old CMOS electronics. Some tell the 180 is built solid as a tank. This is true for the housing, but I already ruined one motherboard just by measuring a line and one daughterboard by fixing a connection.