I would like to keep the planes light, so I am interested in using the smallest battery I can get.

Using a Hextronic 20g 2300kV with a 5x3 prop, I'm expecting something like a 4.5amp current draw.

I'm considering the following two batteries:

Rhino 610mAh 2s 20C/2C 35grams, and

Zippy Compact 800mAh 2s 25C/5C 44g.

Given Flitetest's estimated weights for the planes before batteries (115g), The larger battery would result in a 7% heavier plane. Flight time would be .61Ah*(60min/hr)/4.5a = 8 minutes with the small batt., or 10.7 minutes with the larger.

Which would cause the least frustration; a 7% heavier and therefor faster plane, or an 8 minute flight time instead of 11 minutes (before battery swap)?

Keep in mind these are 7th and 8th graders, so I want them to have something that is as easy to fly as possible. The batteries cost $4.90 and $5.33, so despite our razor thin budget, this is probably not the place to save $0.86 per student.