So my girlfriend bought a 2007 prius about a month ago. First time ever touching a hybrid and working on this car is like trying to learn a new language. So bear with me. The 12v battery in this car died a few times so I bought a new one and probably 2 days went by and the brand new 12v died. It died right when the car was parked so my gf was driving around and when she parked it the 12v was dead. I pulled the battery out to charge it up because thats what im used to doing. Once I go the battery on the charger I grabbed some sand paper and rubbed the terminal, +/- connection wires, and the ground cable connection. After letting the battery charge I put it back in the car and now no lights come on inside the car. Did I do something wrong? I am also wanting to know why the 12v keeps dying. But more importantly how to get the lights back on with the new battery.
There is nothing really special as far as all that goes. It is just the same as any car. If the leads are on firmly and are clean there shouldn't be any problem. What voltage do you read at the front jump point (in the fuse box to the left) under the hood? Is it the same (or similar) to the voltage at the battery terminals? Did you try to jump the car at any time and if you did are you 100% that you never crossed the jumper cables?
If you follow @dolj's good advice and find that the voltage is low at the front jump points, but normal at the battery terminals, the first place to look is at the ground connection to the car's body. It can be loose and/or corroded. Because the 12V doesn't have to crank the engine, it's much smaller than in old fashioned cars, and it's AGM and vented to the outside since it's in the cabin. Otherwise, it's just like any other car battery and you trouble shoot it the same way. If the battery is going flat in between drives, either something is being left on and draining it (a distinct possibility with a recently acquired used car that might have owner-added devices) or it isn't getting driven far enough on each trip to fully charge the 12V battery. Welcome to PC. Hope you can chase it down quickly. I know it's frustrating sometimes.
Even "new" things sometimes fail. A multi-meter would be really helpful in finding the problem. A loose or corroded connection at the FAR end of the main battery cables can be a problem too.
What kind of battery did you buy? If you bought an Optima, that's the problem... They sell fake batteries... Or more accurately they re-sell failed batteries. Zero quality control.
