Assuming we're limiting this discussion to the use of monolights (not bi-voltage) and inverter-type batteries then it all depends on how powerful your strobes are, the output of those strobes when in use, and over what period of time and number of pops you need for one shoot.
I use Elinchrom 600RX's and a 300RX with an Innovatronix Explorer XT SE and an XT.
Depending on the time of day, concept of the shoot and whether I'm using 1 or 2 strobes, that will determine whether I use 1 or 2 batteries. Typically, if I'm using 2 strobes I have a dedicated battery for each one. This gives me the ability to fire at full power, get the fastest recycle times, and the longest battery life. There are days when I'm shooting in 2 or 3 locations over 5 or 6 hours and it's just not convenient to charge a battery, so I need to know I have the juice to make it through the day.
If I power both strobes from a single battery and I'm up around full power then battery life really takes a hit and recycle times are slow.
On the other hand, if I'm shooting late in the afternoon or early evening and I don't need to battle or combat the Sun at all then life is simple and I can power 2 strobes off 1 battery and performance is excellent.
You have to look at the big picture and think about all the variables that make a system workable and affordable, or not.
As an example, yesterday I was shooting with 2 600RX's at full power, in bright Sun, underexposing the ambient light, shooting in 3 locations, and needing almost 600 full power pops plus the pops for metering and white balance.
That's a lot to ask of a portable battery and one wouldn't do it for me.