Noticed my new(er) 2010 was getting mileage in the low 40s. Took a reading from my 4 year old 2010 Prius 12v battery and got a 11.5 reading. Was quite surprised it was reading so low for only 4 years old. I recently replaced my 2008 battery and that was 6 years old with a reading of 11.7 when I changed it out. How strange these batteries vary so much. All they do is start the electronics and nothing more.
As you are probably well aware, the 12V battery is much discussed and debated on the Prius (probably more so than any other component). I think if you charged your battery with a charger, it would likely be fine. The 12V battery will indeed last a long time if you take good care of it. The 12v battery on my 01 lasted until 2011 and even then it was only weak and not dead. Every so often, I put a charger on mine and charge it overnight. I just bought the cheap Schumaker 1.5A charger/maintainer and that does a fine job. I usually do it on a Friday, right after work and leave it charging until the green light comes on (usually about 1pm the next day).
I bought a new battery for it regardless. My fear is my wife being caught behind the wheel and it won't start. She would call AAA and jump start and possibly fry my car. Even with that reading of 11.5 on the 2010, it's driven quite a bit on the highway for over 30 minutes, shouldn't have any problems charging up.
many of the 2010's sat on the lot due to a bad market and battery's ran down enough times to shorten thier lifespan. i bet if you could find out, '10's have had more replacements than most gen II years. battery quality might have been reduced in gen III as well, i'm not sure.
This wasn't the case with my 2010. This was actually a special order one that the customer waited over 2 months to get.
I bought optima's for both. I first ordered from streetsideauto for $147, received a battery from 3/2013 in 12/2013. Thought that was out of line to get a battery almost a year old! 2nd one purchased from Amazon for the same price $147, waiting to see what I get this coming week.
i guess it was something else in your case. if you never drained it, it's kind of surprising, but we only have 3 years of gen III history.
Oh I'm unsure if this battery has been drained, the old owner I purchased this from wasn't exactly a car person. This may very well be the cause of the premature low readings. He did all the maintenance at the dealer but he left all the nicks and scratches (even a dent in the fender) on the car untouched. I did notice he left the headlights on at all times, the car would shut it off automatically but they are always running when the car is on.
