I use a UK version of the Vaquero (Trident 11 Extreme) which is basically the steroid version if you like,been tweaked by the main UK Tesoro/Laser repair centre and also a main dealer,it would have originally been made and shipped over with the 1 9volt battery,but i am assuming as its been tweaked for better performance it has had the Tejon battery pack installed for longer battery life which is of course 8x1.5v +12v,in this configuration it last alot longer than just the 1 9volt battery by a massive margin.
Also another bonus that i have found with this setup is that the original battery compartment is of course still on the machine but disconnected,but i store a spare new battery for my Garrett pinpointer in the battery compartment and so i never forget a battery for the probe as i would be lost without it other wise.
Cannot comment on how long a normal Vaquero battery would last but having the Tejon battery setup was a smart move in my opinion.