This means that the battery is discharged down to 10.5 volts over a 20 hour period while the total actual amp-hours that it supplies are measured. Sometimes ratings at the 6 hour rate and 100 hour rate are also given for comparison and for different applications.
Pool meets are usually no more than 4 hours, but beach meets last about 7 hours. It depends how many events are in the meet. And then if it is a really big meet (like a tournament kind of) it can last days. Hope that helps.
You should be able to run 3 miles under 21 minutes prior to starting basic training. Swimming: You will swim everyday during the Indoctrination Course. A trainee may swim 2000 meters or more in a typical session. In preparation, you should swim 500-1000 meters, 3-5 times per week.