Interesting topic and I found the answer by
@JimD. to be exactly what I use if I have to fly continuously on a job with one of my
P4P V 2.0s or RTK. It’s not based on any great scientific method that I came up with that number, I’m just conservative and I like to make all my gear last including my batteries.
My thought process is based on the old “let your battery cool for as long as you used it before charging” mind set.
I line up 9 batteries, I pick up battery 1 and insert it in the aircraft and fly for around 20 minutes up to RTH, on landing it could be anywhere between 25% and 35% depending on conditions and the flight profile.
I remove the battery 1 and place it down to cool and insert and fly battery 2, on landing I remove battery 2 and place it down to cool, put battery 1 on charge and insert battery 3 and fly
Wash, lather, repeat inserting a new battery, placing the just flown battery down to cool and putting the previous battery on charge with each flight. I use two multi chargers and can have 6 batteries charging at peak.
By that method I find that 9 batteries keeps me in the air all day with a little wriggle room for the battery that’s just come off charge to cool a little before going into the aircraft and gives me peace of mind that I’m not remotely abusing my batteries.
So 3 aircraft .. 27 batteries by that method.
Regards
Ari