2007 with 45K miles - failing HV battery?

My uneducated guess is that it sounds normal to me. The 12v is easy to check.

 

You will not be able to make the Prius READY if the traction battery fails completely.

 

This will be clearer if you use the terms HV Battery and 12 v battery (or similar) as they are different beasts with different solutions.

Your HV battery is under 100% warranty for at least 8 years or 100,000 miles. If it fails it will spit out a bunch of codes (usually well in advance of total failure) that the mechanic can read. (or you with the right scanner)

Your 12 v battery has an average life of about 4 years (about now for 2007) and will cause a number of symptoms as it fails. (reduced Mileage, slow power windows with the car not in READY, Odd error lights, etc.) There is a built in battery test page, or you can test with a multimeter before the car starts in the morning.

http://priuschat.com/forums/gen-ii-...out-switching-headlights-off.html#post1095046

http://www.elearnaid.com/12vo1topraub.html

 

Just as an experiment could you try letting your car warm up (idle in park) for about 45 sec to 1 min before driving and see how much difference this makes. The Prius often tries to use the HV battery a lot more when the engine is very cold.

 

No, 14.2V is about right for the battery being charged from the HV battery through the DC-DC converter. Most people report around 13.8 to 14.2 here, it probably depends on the 12V battery condition. Yours sounds like it's starting to get a bit marginal, so yeah that's probably one source of drain on your HV battery at start up - the HV battery trying to get some charge into the 12V battery ASAP.

Basically the more your voltage fluctuates in this test then generally the worse condidtion it's in. Mine is actually in a fairly similar condition to yours and needs replacing soon. Starts at about 12.3 volts, drops to about 11.8 for a second when going to ig-on, but then recovers to about 12.0. Goes to about 14.1 when I go to "ready" but if I leave it for a few minutes it will ease back to 14.0 or even 13.9. I'll be getting a new one before winter (which is next June down here).

 

Don't forget to try the warm-up test i mentioned above. The load on the HV battery during the first few minutes can be greatly effected by how you drive while it's warming up and how cold it is. So changes in the climate and how you drive can make a big difference to how well the HV battery keeps it's SOC.

Have a go at letting it idle (in P) for about 60 seconds before you drive and see if it helps to stop the SOC from dropping too fast.

 

Sounds like you are due for a 12v. One day you may find the door needs to be unlocked manually. Then you'll discover the cockpit is dark. Then, if you are lucky, you may be able to get the car started after 3 attempts. Then you'll drive to the dealer to buy a battery.