Lithium lon battery has a capacity of 2150?

Question

a lithium lon battery has a capacity of 2150 mAh if it is conneted to a device which draws30 mA approximately how long will the battery last?

Answer 1

2150 milliamp per hour
2150 ma/h divided 30 ma=71.67 hours
but that is ideally;however, a battery discharges in an exponential curve so useful life will be about 3/5 of 71.67 hours or about 43 hours.
or i could be wrong