How many batteries do you have, what size and what size is your converter in amps??
Assuming your converter provides amps equivilent to 20% of your battery bank amp hour rating ( i.e. 40 amps for 200amp hour battery bank) ... AND you never let the voltmeter drop below 12.0V IN USE... then you should be able to get to 90% charge in around 3 hours of charger time on the generator. Getting to 100% will take HOURS more and you can do that when you plug in back at home IF you are limiting yourself to 3-4 days of boondocking with nightly or daily runs of the genny for at least 3 hours. If you have a long drive home and the TT alternator charges your batts as well...then you could be charge when you get home to 100%.
To check...disconnect negative battery wire for 24 hours...then reconnect and read your voltmeter. It should read 12.6 without being plugged in to anything for 24 hours.
If not...charge it up. Under charging is a big killer of batteries just as discharging below 50% (12.2V...static reading not in use).
If you boondock a lot...the Victron will pay for itself in genny gas and maintenance and in replacement batteries that have been murdered. Otherwise...muddle through with the voltmeter...and keep the water up and don't run the batts down too far and always charge to 100% at the end of every short trip.
Most people think their batteries can power things longer than they can and don't realize the amps being used. If you don't boondock much...like me now...you don't need monitor for the occasional short stay. But if your batteries die early...you probably should consider one.