Weird battery issue: restarting clock, wiping settings?

I assume that you checked the battery cables are secured?

 

The clock and radio presets resetting indicate a low 12V supply, even though the battery was changed in January. If you drive short distances you may not be charging the 12V battery enough.

Check your 12V battery after the car has been off for at least 2 hours, overnight is best. If it is less than 12.0V it needs charging.

A loose battery connection, as indicated above, could also be a problem.

 

Regardless of whether the 12V battery was replaced in January, I agree that the two most likely reasons for your problems are that 1) the battery is bad (or desperately needs recharging) or 2) a battery cable connection is loose.

Since the battery was replaced 5 months ago, it should be under warranty.

 

These guys are spot on. For some reason dealers seem to have a hard time properly testing the Prius 12v. It wouldn't be the first defective battery ever. Also, loose battery cable connections could cause the same issue.

 

Please run the test at Weird stuff happening? MPGs dropping? Test The Battery | PriusChat after the car has sat MANY hours or overnight (or you can use a voltmeter). Please tell us the 3 values (not just 1). Don't go changing the battery first until you tell us the values...

If you have HIDs, you can avoid unnecessary cycles on the lights by toggling between off and parking light positions.

Weird stuff can start happening w/a low or bad 12 volt. Don't waste $ on having a dealer "test" the 12 volt (07 Prius Dead - Any Guesses? | PriusChat). Since the 12 volt was replaced recently, it's unlikely it's bad.

Assuming there isn't a loose connection, if you've run the battery flat and you don't keep the car in READY mode long ago (driving around or not doesn't matter), the 12 volt may not be getting recharged sufficiently since the Prius charges the 12 volt very slowly.

 

I know this reply is beyond late but for those who are suffering from the same problem I might have a solution for you. The first thing you want to do is make sure that both terminals of the battery are properly sanded and dieletric goo or vaseline is added to ensure a good connection. The second thing is to completely unbolt the negative cable from the body of the car. Where the negative cable meets the body of the car you will find a rust spot or a corroded spot that will need to be sanded until you see nothing but shiny metal. Then properly tighten all the connections. This should get you going. Best of luck.