How to be sure my prius battery is going bad?

My battery warning light came on yesterday leaving work on my 2002 prius with 71,000 miles.. I drove the car for about 10 minutes with no issues. I brought the car to the toyota dealer and their diagnostic test came up with codes P3000, P3009, C1202, c1521, c1522. They wanted to do more tests with more money and i drove the car home after 100.00 bill. they said i need a new battery and computer assy with a charge of 4,400. Are they kidding. the car drove home no problems and the warning light was not on. does this mean the battery is starting to go bye bye?