My standard approach for replacement of batteries that support NVRAM containing instrument calibration , etc. is to connect either another battery or external power supply **with floating outputs** through a 1K ohm resistor to the PWB traces elsewhere on the board, usually after a reverse flow blocking diode in the battery circuit if it is present. Then removal of the old battery is easy without losing the contents of the RAM. The 1K resistor is just a precaution to keep from drawing high currents or other possible issues if you happen to connect to a wrong part of the circuit with the external power supply.
If one chooses to try the instrument power-up approach as you had mentioned make certain that you use a soldering iron that is not connected to third wire ground or has the tip grounded otherwise or else you will short out the battery and kill the RAM contents. Use of a battery powered soldering iron also allows safe removal of the battery. But that offers no help if a vacuum desoldering iron is required of which it frequently is.
Greg
