The file is annotated.  Edit it to specify the voltage channel ("Cels", "Cel-", etc. ) and the physical switch ("sa", "sb", etc.) or logical switch ("ls1", "ls2", etc.) you want to use to activate the voice announcement.  Then set up a SF that plays this script when the switch is active.

You may also want to edit the variable delay_val, which is the minimum delay between announcements.  Mine is set at 5 sec, which works for two different kinds of announcements.  I have a momentary switch short pull LS that will play a single voltage announcement.  I also have a LS triggered by hitting the minimum cell landing voltage, which repeats every 5 secs.  You can change this interval to whatever you want, but you need a non-zero value here to avoid multiple announcements for every switch activation, due to the loop speed.  

Put the script in SD/SCRIPTS/FUNCTIONS. Note that if you activate without any telemetry inputs (including in Taranis simulator), you will only hear "zero zero volts". You need a non-nil 2-decimal value in the channel buffer for it to work correctly.  If you have problems getting Companion 2.1.3 to see the file, try putting a second copy in your SD/SCRIPTS folder and reloading the model file.  Once it gets mapped as an available script, you can delete the second copy (strange but it works for me).

V1.1 REVISION:  File name shortened.  Logic reorganized slightly to make modification easier.  No functional changes.

Have fun.