After 180,000 miles and almost 8 years of service, I replaced the 12 volt.

I picked up a 2011 Toyota-certified with 77,000 miles on it 3 months ago, car is great!

http://www.autoguide.com/auto-news/2014/12/are-hybrids-reliable-.html

 

That seems like a logical assumption but it's wrong on two counts:
A failing 12 V battery can make the DC-DC converter run a bit more (there is no alternator like in a conventional car).
It can also cause various electrical computer signals to be just a tad bit different, causing all kinds of strange things......including declining mileage.

Your basic theory is right though as running the AC compressor consumes a fair amount of power and it does make a slight difference in the mileage.

P.S. You are VERY lucky that the 12 V battery lasted 8 years. With a conventional wet cell, I start getting nervous around 4 years and with an AGM around 6 or 7.

 

Hi Easy,

Your replies to posters on this subject still confuse me.

The gentleman said basically that he changed the 12 V battery and now observes that he has an improvement in fuel economy.

You said the gentleman was wrong on two counts, then you say:

• A failing 12 V battery can make the DC-DC converter run a bit more;
• It can also cause ... declining mileage.

So, apart from the gentleman calling the DC-DC converter an alternator, what exactly was the wrong information?

 

great experience o/p, keep it up! they don't make batteries like they used to.

 

Going to go pre-emptive on the 12V after Christmas. 2008 with 83K on it has the original 12V in it, I believe. Haven't tested it except via the on-board diagnostics. Still seems good, but I gotta believe it's very close to death.

 

I thought I covered that.
The extra load of trying to charge a dying battery is probably not the ONLY thing that causes the lower mileage.
As a matter of fact, a 12 V battery going bad often will LOOK fully charged when it is not and thus make less load on the charging system not more.
The mileage difference probably comes more from the computer boards having a slight malfunction because of low voltage.

 

That makes sense.

Thanks.

 

Good to hear the factory battery holding up so long.

 

It will, if it is not abused via driver error such as leaving a cabin overhead light on. The OPs situation is ideal for 12V battery longevity: ~23K miles logged annually which results in substantial charging time for that battery.

 

To all those in the know -

After the car sat overnight outside, my 12v battery reads 11.9 - 12.2v depending on how cold it was. With Accessory On, it's 11.5 - 11.8v.

At what voltage should I replace the 12v battery?

Thanks!

 

NOW.
You start out at 12,.6-12.8 presumably, and just sitting overnight should not drop it much if any.
That depends a little on how cold it is when the measurement is taken but I think you are right on the verge.
I start getting nervous at 12.4 no load and 12.0 in ACC.

 

Since I don't drive 20+k miles annually, I hope to get 7 years out of mine.

 

If you don't drive enough to keep the 12 V in good condition, then you just need to get into the regime of monitoring the battery and externally charging as necessary.

 

thanks!

 

2005 Prius, 188,444 miles, 12V battery is 9-1/2 years old but getting weak.

 

9.5 years. Wow, I thought 8 years was stretching it for some. You should definitely go shopping NOW.

 

you have about the same as my daughter, she has no intention of replacing hers, but it probably won't last more than a few more years. it's not likely close to death, unless someone has run it down.

 

Yeah...did it last week. Glad I did. Voltage of new battery is a reassuring improvement over what the older was getting. Expect it to go down the road for many years now. As long as she keeps it between the lines, I've done everything that should be done to it at this mileage.