Lexus RX 300 battery problem or alternator???

What is your question?

We placed the battery June 2009, with a new one from Costco. Lately, I have been noticing that the clock reverts to 1:00am, which is what happpens when the battery gets disconnected, yesterday the car wouldn't start, my neighbor gave me a jump & checked the volts @ 13.87 today he rechecked them & they were at 10. something...could it be the battery or is it a short or the alternator, how can I find out?