2005 Prius 12 Volt Battery Failure Experience

welcome! you're not supposed to replace it every four years. that would be a waste of money. replace it when it's getting weak. below 12.4 volts. regular checks with a volt meter are sufficient after 4 years, but if you ever run the battery down by leaving a door open, you should start checking it after that.

thanks for the write up!

 

same here. i've read that as well, but i think it's a bit absurd. my batteries have always lasted 7 or 8 years. and they ain't cheap!

 

"I've read that you're supposed to replace the 12 volt battery every 4 years but I swear the one I removed looked stock."

LOLROF! Judging a battery by the way it looks! Batteries are designed to last 4-5 years. If you fully drain them (you know, leave the lights on or the door ajar overnight) battery life is further shortened. Warnings are posted frequently here about the many MANY problems associated with dead batteries. Do you also wait for your car to run out of gas or brakes to fail or wheels to fall off, before you do preventative/scheduled maintenance?

 

I've been reading this and similar posts as I have been trying to figure out what I may need to do to keep my 2008 prius, that I just purchased used with 188,000 mi, going strong. If it wasn't 1220 am I'd go out and check my 12v right now Im so concerned, I caught a glimpse of the 12v the other day and I saw the Panasonic name on it....could this be an original battery? I will try to explore further in the AM for a date and to try to get my car in maintenance mode...

 

If you care to determine the age of the replaced battery, there is no need to guess. A date code is located on the top of the battery, near the center. That code is obscured when the battery is installed as the bracket covers it, but once the battery is removed it is easy to see.

The GS Yuasa battery which is Prius original equipment is also sold by Toyota dealers. Those replacement batteries also come with the Toyota TrueStart sticker and the batteries have an 84 month pro-rated warranty.
http://www.toyota.com/toyota-owners-online-theme/pdf/Batteries2011-LowRes.pdf

Regarding preventive maintenance and 12V battery life, some owners are content to wait for a failure before taking action. You sometimes see those owners on the side of the road with their car's hood up. Or, stuck in a parking lot.

There are many posts from owners who waited for the 12V battery to fail. Then either they or a well-meaning Good Samaritan jump start the car using reversed battery polarity, which at minimum causes the 100A DC/DC fusible link to fail (which requires removal of the main relay/fuse box to replace) and sometimes causes the inverter to fail. Then if they have to rely upon dealer service to install a new inverter, the repair bill is well into four-digits.

Other owners like to have a car which is actually reliable. Those in the latter category may find it useful to keep an eye on the condition of the 12V battery, among other components... If the car is lightly driven then it is a good idea to charge the battery periodically, once or twice a month. If that is too much trouble then replacing the battery before it fails can be a good strategy. If you live in an area with snowy winters then a 4-year replacement cycle for the battery may work well.

Measuring the voltage across the 12V battery is a test that can cause "false negative" results. In other words, if you measure a low voltage such as 12.1V or less, that is reasonable proof that the battery is bad, or at minimum discharged and needs to be fully-charged.

However if you measure 12.5V, that is not an absolute guarantee the battery is good, if that measurement is taken immediately after the car has been in use. The voltage reading will be artificially high due to "surface charge". After the battery has rested overnight, the voltage reading will be more accurate.

A new 12V AGM battery should measure 13V, out of the box. If it does not then the battery should be fully-charged before installation, and the low voltage reading offers some evidence the battery had been sitting around for months prior to your purchase.

 

Apologies for my sharp reaction, but there are many interesting threads on Prius batteries. BritPrius's is partcularly unique in his suggestion to use wheelchair batteries. Reading the warranties on the PDF, the new Toyota TrueStart battery now has an 84 month warranty with a "simple two tier" 60 month proration and a 24 month free replacement. The other (not available for Prius) has a 60 month 42 month proration and 18 month free replacement. Anyone know how the "simple two tier works--what's with the 84/60 numbers? FYI: The 2005 Prius came with prorated batteries that were worth nothing at 3-4 years or so the dealer told me, back then.

 

In regards to Patrick's post/response, is it possible to remove the bracket that obstructs the code without disconnecting the battery? I don't want to lose all my settings just to check and I don't have an extra battery to hook up under the hood. Also is there a date code on there no matter what brand? I had a battery on my ford escape that had no disernable code until I called the manufactuer

 

What was happening in this case is the dead cell in the 12V battery was drawing excess current from the inverter causing the observed symptoms. The inverter couldn't keep up with the initial draw.

 

The GS Yuasa battery has a date code in DDMMYY format. The positive battery cable has a plastic fitting that is attached to the battery bracket, and it may not be easy to remove the bracket while the connector remains attached to the positive terminal.

Many other batteries have a two character date code sticker where the first character is alpha and corresponds to the month while the second character is a digit and corresponds to the year. That sticker usually is on the top of the battery case.

Given your experience with the Ford Escape, I agree that it is not guaranteed that a sticker will be present or that it will be obvious how to read the code if one exists. My Ford Mustang has a Motorcraft battery and it is not obvious what the date code is.

 

i live in a snowy area, and have never had a problem with my 12 volt batteries (3). i maintain that as long as you don't drain them accidentally, or drive so little that they don't get properly charged, and they weren't drained before you took delivery, you won't have a problem for a good long time. way more than 4 years.
and my first two gave plenty of warnings before the car wouldn't make ready.

 

That's great to see that you are alert enough to recognize the warnings when they occur, such as dimming cabin lights for example. Not everyone is as responsive to their car's changed behavior as you might be. The OP had two warnings before the battery finally died, which is additional evidence that if you can recognize the changed behavior and quickly take the appropriate action, then no worries.

 

agreed, and that can be said about many things in life. and that's why we have dealers eager to replace anything and everything for the unaware.

 

Said the man with a 2012 model...lots of ifs in the above statement. For the rest of mere mortals, a car battery is still a car battery. It needs to be changed as part of a regular maintenance schedule.

 

my 2004 started acting funny in 2012. remote issues and the like. my 2008 is still going strong under my daughters usage. i can clarify more if needed.

as for my 2012, it will be four years old on april 26th. although it had probably already been built by now, since they shipped it from japan. it has been sitting in my cold garage since february 18th, but i know it will be fine when i get home, like all my others were. why would i proactively dump it in the environment for a new one?

 

Using that logic why would you change your oil or tires? Why not wait until failure? Get stuck on the side of road with flats or a blown engine? The key word is "preventative".

 

okay, to each his own.