A: Press and hold the on/off button. Your GEM™2000 will shut off in 15 seconds or less.
A: About 8 hours. This is assuming a pump running time of 120 seconds, and a "normal" well field. Of course, your time will vary with such factors as the age of your battery, the number of actual wellheads you read and their type, and so on.
A: No. GA mode mimics the operation of the GA90, which is used only to sample gas composition, not to measure flow.