It should last a very long session easy, the old one with 3 rechargeable AAA batteries in it, i easy do 8 hour shooting sessions. My problem are more my phone being very close to wanting to start battery saver in the end of the day.
The V2 have a build in battery, so it can also go on a charger and also while shooting if you are able to deal with the wire. In the V1 i have to remove the 3 AAA batteries and put them in a charger, but i do have 4 sets of batteries.