need advice on 10 month old replacement 12v battery

Yes that 11.8 is disturbing and your right to be concerned
that it might leave you but if its the stock Prius battery its not that great of a battery to begin with. I'm on my third year of my oem battery on my 07 and I its hitting about 12.00 too even though I have taken very good care of it including periodic battery tender charges and its never been subjected to cold or never needed a jump. Time for a new battery for me too.

In your case cold is tough on batteries. Especially really small not so great batteries.

But just like the oem tires...Until you move up a notch in quality on your own dime you'll never be happy. The good set up is the Optima Yellowtop battery. Thats my next purchase. Best buy is from elearnaid.com.

Like the tires move up to a quality part and never look back.

 

It's possible that low temperature is a factor here. If the temperature of your battery was 33F when you starting taking measurements, and your car has been sitting for a couple of days, the low readings that you recorded are plausible. Batteries are not covered by the Platinum warranty, but I think they have their own 24 month warranty.

 

dvikib,

:welcome: to PRIUSchat. :cheer2:

+1 on what's already been said.

As to the 3.5 year life on the OEM battery, expected service life is ~4
years. Extreme heat and cold reduce that somewhat. We don't see much
of the extended 100+ degF temps of the folks in Arizona, or the 0- degF
temps of the folks in Canada here in Ballamer. Lately our temps have
been lower than usual, but not in a really big way. So, I think something
is not quite right.

It looks like you may be in the relatively rare situation of your Prius not
being driven enough to keep the 12V battery well charged. At 23K
miles at 4 years old that's less than 6K miles/year...

To cause any meaningful change in the charge of the 12V battery, you
have to drive for a long time. If you drive daily for, lets say 2 hrs like I
do, the 12V battery seems to be OK. (I'm putting ~17K miles/year on
my '08.) So, you may need to put your 12V battery on a charge tender
frequently. Something like this, not a trickle charger.

Also, things are not looking good with the new dealer installed 12V
battery. You don't say how long you've had it. I'm presuming less than
a year. You should be seeing ~12.5V after the car sits unused
overnight. It is possible that the dealer did not fully charge the battery
before it was installed. No way to prove this unless you asked for a
copy of a battery status report when it was put in. The low reading may
also just be a reflection of how little the car is driven and resultant low
12V charging via the onboard DC-to-DC converter.

FWIW, of the three dealers I have used for routine service in the
NW/NE Ballamer area, I have settled on Billl Kidds Toyota in Cockeysville
as the most reliable. But even there, I have learned I need to be very
clear on what I want when I go in.

By the way, you did a good job of providing info on your situation in a
first post. Well done.

 

unless you had multiple issues with the battery, u probably should not have replaced it. my 2006 the battery has died 4-5 times. each time it was user error. i simply jumped it and it went on just fine. (i am not primary user of car)

now, my 2010 Prius died one day as well. still not wholly sure why it happened. now it was during a period where it sat for approximately 8=10 days... dont remember how long it was now, but a battery dying that fast should not happen.

now, the Prius has a vacation mode that is supposed to turn off the doors and whatnot after a few days but i think that was not working because it was parked next to the SPM and my walking by it all the time probably kept it active.

either way, that happened several months ago and have had no issues since then

 

I would watch for any unusual behavior but would not replace the battery solely because of those readings.

Do you *always* lock the car, no matter where you park it?

 

Your numbers are low enough so that you should connect a battery charger to the 12V battery, charge up the battery overnight, and see if the voltage measurements improve a few hours after you have disconnected the charger.

If the measurements improve, then no worries. If they remain around the same, then I suggest that you consider replacing the 12V battery soon. I believe that the battery may be covered under the Toyota parts warranty, since it is only 10 months old.

 

If you attempt to recharge the battery, don't trust volt meter readings immediately thereafter, they'll tend to read higher due to surface charge or something like that. After charging, I'd drive it for a day, and then check voltage. Ambient temperature will also affect voltage reading, but as long you're in a sheltered garage and above zero I don't believe it's a big factor. A "good" battery should be around 12.6 volt or higher.

FWIW, I would only spend so much time flogging this dead horse: if the battery's had repeated partial drains, it's day's are numbered. Look at it like tires with tread depth approaching minimum: how much do you want to push it?

Just as an example, emergency response vehicles will just replace their batteries periodically, every two years, even every year. Obviously that's a bit extreme, but the principal is sound: if you don't want hassles just replace it when it's given you decent use, before it croaks.

Also, just my 2 cents, I'd go with the stock battery. One way to insure against future partial drains: just shut down the interior lights that "auto" shut-off, completely.

 

Be warned that all batteries have a temperature coefficient. The Prius 12v battery is a lead acid calcium type which looses significant capacity when the temperature drops. This also changes the charge characteristics such that the charge voltage needs to be higher in order to complete a charge. Since the Prius doesn't have a temperature compensation circuit, it's twice the problem in cold weather; not only does the battery have less capacity, but it never gets a full charge.

A typical 12V battery of the same type as in the Prius has a typical charge voltage temperature coefficient of about -12mV/°C. This means when the temperature drops, the charge voltage will need to be increased by 12mv for each degree C the temperature drops.

I recommend you apply an external charger with either a temperature compensation circuit, or one that at least has a charge voltage high enough to actually give the battery a complete charge.

 

I ended up getting this charger....
http://www.amazon.com/dp/product/B000FQBWCY?tag=priuschatcom-20 only does it do a nice job on topping off the Prius battery when I do not drive it for extended periods, but when not helping the Prius, it sits on my 4Runner battery 24/7 and keeps the battey ready to go! It comes with various adapters to help move it from car to suv!

 

any lead acid battery creates a float charge situation and charging manually should not be necessary. what i would do is drive the car around for at least 20-30 minutes. then park it. wait 3-4 hours then check it.

if you manually charge it, you probably will have to wait at least 8 hours and for true results you should disconnect it from the vehicle as there are vampire drains on the 12 volt system that can vary widely. i believe this to be way more of a hassle than its worth.

if you are truly concerned about the 12 volt system. i think it would be easier to maintain one of those sealed 12 volt jump box. many now come with emergency flasher, air compressors, etc. so very handy for many things. i use mine as a charger for my cellphone on camping trips and such.

if you do do this, remember to boost charge it at least weekly

 

The Jump Box with accessories is heavy. I got the Peak 300 at Pepboys. It's $24 after Rebate. Sometimes cheaper. This thing is surprisingly light.
I bought a $10(on sale) Marine Float Charger from Harbor Freight Tools for general use. Never used it for my Prius but on a truck. I could make my own pigtails for $4 bucks. "Cheapo" battery tender. Battery Tender Jr is around $25. Found on Amazon.
BTW, since the battery is in the trunk, wouldn't the car drain slightly more from the 12v battery since it's activating the door sensor system even without the dome light being on?

 

Your replacement battery has a 1 year unlimited mileage warranty.