The other day my daughter was driving her 2005 Prius when just about every idot light in the dash came on. The big red trinangle and in the MFD the yellow one with the front of a car back to back where the main one's. Did the MFD voltage test after it sat overnight it read power button pushed once 12.1v. With PB pushed two times ACC mode 11.9. Foot on brake 11.8v. PB pushed and foot on brake started 14.2. Running headlights on 14.2v. So today checked again all idot lights have gone off and it checked the same voltage. Drove it a little bit today ans noticed my miles per gallon where way low like 26mph was the highest. Now this is the original battery, could it still be showing good? But still actually be going bad? And would it affect my mph that much? Should I drive it a few more day's and see what happens? Thanks Tommy
The 12V battery sounds fairly normal - it shouldn't have caused all of the warning lights. You may want to have the codes read to look for problems. Tom
It's still the original battery? Replace it. It's running on borrowed time. And yes, a weak/bad 12v battery can have a negative affect on your MPGs.
If the lights came on while your daughter was actually driving it has nothing to do with the 12v battery, as once the Prius is made ready the 12v battery can be removed and every thing will still run fine. The DC to DC converter runs everything once the car is ready and it provides all the power for the 12v systems including charging the 12v battery. It is possible you have a HV battery problem but this should through fault codes.
Thanks for all the replys put in a new optima yellow top battery and so far everything is back to normal and running fine.
