2010 - Sudden 12V Battery Failure

Also those figures indicate that your new battery is an AGM and the one in the wife's car is not.
The AGMs run about .3 to .4 higher.

The 12.34 would give me mild concern and cause me to charge it good and keep an eye on it.
It could be on the way out.

 

My 2008 prius battery shows 9.3v in onscreen diagnostic mode from cold overnight startup ( accessories boot up - not activating powertrain battery system ), this will creep up to 9.6v after 2 mins or so then when I activate the powertrain batteries it goes to 12.3 then after petrol engine start it shows 14.4v so no problem with dc invertor system however after an hour of town driving the 12v battery reports 10.4v ( I believe this is what is called a 'float charge' which did drop back to 9.3 after 3 mins or so. After perusing several websites I am led to believe that the optima 8171-767 is the ideal replacement for the prius - or any glass mat battery that fits & that holds at least 38ah and has good deep cycle recovery ( crank amps obviously not applicable in this case ).
I am currently fishing around for the best deal on a good battery as I know fine well I should not be driving with the aux 12v battery in this state - but just saying it still works...for now

 

The dealer parts dept was cheaper than AutoZone/advance for me. It was not that difficult to change it.

 

Thanks for the info - I have fitted a standard 45AH float acid battery ( cost £54 ) but before I removed the connections I hooked up an old spare 12v battery to the fusebox jumpstart connector in the engine bay with jumpleads so that the computer did not require a system reset while I done the battery swap over in the boot. In regard to the tiny vent tube for the 12v battery ( for which cannot be fitted to the one I have installed ) I am led to believe that the amount of hydro gas that is actually emitted during normal use ( not forgetting that this battery is used as a system support supply & not an engine turnover high amp one ) is so scarce that the chances of it even encroaching into the passenger compartment are very extremely remote & will be taken up by the passive updraft of the traction battery ventalation assembly - I also considered toyota safety concerns of using glass mat battery as opposed to float ( standard ) in case of severe side impact causing acid to leak into passenger area - well with respect to that issue I am of the opinion that if such damage occured then you would be more worried about all the HV connections frying your nice person ( yes the powertrain NMH battery bank under the rear passenger seats ) than one small lead acid battery tucked away in the lower regions of the boot. Furthermore I have purchased a small 12v motorcycle battery (12AH) for £20 which I keep in the boot compartment lower left hand side ( ie mirror image area for where the 12v battery is ) this battery is no larger than 3 blocks of soap so with a set of jump leads in the boot I have a spare means of getting 'started' if the main 12v battery fails - apparently the extra space in the opposite lower boot area can accomodate a full sized battery which can be hooked up by means of a switch in the existing wire loom but I have not looked into the exact details as yet.

 

I managed to run ours down overnight. Yesterday afternoon, around 3:30 pm, left the drivers door open, gonna claim grandkid distraction. It sat thus till around 10:30 am this morning, so maybe 19 hours. I have the dome light shut off, but the good 'ol door courtesy light (switchless) was going all that time. Also the two little sneaking lights under the dash (also switchless). The voltage had been floating around 12.5; when I checked this morning it was at 11.9.

It's been hooked up to the CTEK 3300 from around 11 am, coming up on 5 hours soon. CTEK still showing charging. That's not unusual; I hope it gives me green light (battery charged) by bedtime tonight.

I'm maybe going to look into disconnecting those damn courtesy lights and underdash lights. I don't like monkeying with non-switchable lights, but this is war, lol.

 

suggestion - you could remove the doorlights by gently prising the facia covers to get them out, as for the under the dashlights you must have a different model from mine ( mkII prius 2008 ). If your battery reports anything under 12.5 from a cold start then it has a dead or failing cell - all lead acid batteries have what is called a 'float charge' ie not the real potential ( especially after being charged ) which can be tested by a meter from cold or by keeping your finger pressed on the display button after pressing the start button once whilst turning the sidelights on/off 3 times to get into diagnostic mode then press menu then vehicle signal check then you have the real voltage from the 12v battery - exit from menu by holding down display dutton for 5 secs or press start button to reboot ( check utube for details if unsure ). Also do not put any metal stuff in the dome light compartment holder it makes the internal alarm sensor go nuts after a few hours ( been there done that !! ).
Bottom line - get a new battery - it aint have to be the toyota spec - just one that fits - thats what I done.

 

Well I'm hoping the CTEK will pull it back up. Dang.

If and when I replace I'll go with Yuasa thru dealership parts dept, it something like $210 (can). I can get rebranded Exide thro Canadian Tire for about $185, but they're in-stock qty all ways is the same, I don't trust their freshness.

 

After about 11 hours the CTEK dubbed it good. I checked voltage: 13.01. For sure that's falsely high: we've got an extended drive day, Coquitlam to Steveston, so that should be good for it. And a voltage check post-drive will be more realistic.

I'm under no delusion that it's completely restored though, every deep drain takes a toll.

 

It has a lot less to do with some sort of conspiracy to make stuff crappier and cheaper and simply people's expectations that things WILL get cheaper. WallMart comes along and sources some battery from the uttermost cheapest Chinese supplier that is willing to fill them with dog pee because they know if they sell it for $42.99 people will suck them up instead of buying the actual quality $100 battery that will last. Everyone else has no choice, they all follow suit. Likewise the car manufacturers learn to cut here and there where it is least noticed because lots of small numbers adds up to big numbers and the competition today is mainly on price for most things.

Beyond that though you have to be realistic about lead-acid batteries. I know a thing or two about battery tech, and basically a lead-acid battery, discharged to under 50% and with fairly optimum charge and discharge rates is likely to last somewhere on the order of about 1,000 cycles. What the OP experienced is classic behavior. The plates break down, and eventually one of them FALLS APART and begins to intermittently bridge a cell, or else material simply bridges across. The material creates shorts, which burn so they come and go and the battery may seem to work fine and then suddenly draw a whole lot of current, drop voltage, etc. And in any case it will be holding a smaller charge (by maybe up to 50 or even 70% after 5 years and presumably pushing 2000 cycles). Even in the old days most people were told to replace their car battery every 2-3 years because 365 * 3 = 1000 and you're starting to push it. You can usually get 5 years out of a battery, even decent ones today, but you are still pushing it.

 

Hey, wait a minute.
Let's not insult Chinese dogs, OK.
They need jobs too.

Welcome to the forum.

 

fair enough, the poor things hardly get a break as it is...

Anyway, I don't think batteries HAVE actually 'gotten worse' over the years. They always lasted maybe 5 years, but back in the 'good old days' you had to check your electrolyte levels every so often. Also VRLA (gel or AGM) batteries are NOT as reliable as the standard flooded L-A battery. They are more easily damaged by poor charging and in general don't do as well under heavy loads. In the Prius application, where the battery is just used for aux power its probably a better solution than a flooded battery (presumably Toyota isn't stupid). It still may not have the long-term lifespan that some people are used to with car batteries. OTOH I think its a better choice for a battery located inside the passenger compartment (though nowadays there are certainly plenty of manufacturers locating flooded L-A batteries in the trunks of cars).

Basically, replace your battery every 3-4 years, certainly do so if you note any decrease in charged voltage, significant voltage drops when partially discharged, etc. I see that the 'yellow top' battery is a little expensive, but its not that bad (you can currently get one for under $150 online, though I guess you risk getting an old battery).

 

I don't think it is proper to lump gel and AGM together for analysis purposes. They are somewhat different.

And I don't agree with your statement in general as it applies to an AGM battery used in a properly designed system......which I think you can assume most cars these days are.

My personal experience and all of the reports I've heard says that a conventional wet cell battery is usually good for ~4 years but a decent AGM will last twice as long.......and with less care too.

They are even making "deep cycle" AGM batteries now. Expensive though and in that kind of an application I haven't seen any reports or evidence that they are really much better.

 

I measured about 0.7 amperes drain with a door ajar and no lights on. 19 hours times 0.7A shouldn't completely deflate a healthy battery, but you had all those silly lights attacking the battery too. Disconnecting the useless lights on the doors (as Ally suggests; it's easy!) was my very first improvement to the Prius, as soon as I got it home from the dealer.

 

Yeah, I don't like to start prying things out, disconnecting leads, it's just more stuff to remember, come trade-in or sale time. But I'm tempted...

Plus, our battery's getting a little long in the tooth.

And oh yeah, beside the door courtesy light, we have the illuminated door sills (big whoop) and little lights under the dash board, illuminating down by your feet (everyone has those?).

 

just to let u all know my new replacement flooded lead acid battery is working fine ( yes I choose not to go with toyota safety guidelines for agm or gel battery ) £54. Also purchased a very small 12v/12AH sealed lead acid battery for £23 which I keep in the empty boot space compartment directly opposite ie left hand rear wheel lower bay along with jump leads tucked in the spare tyre bay so I have an emergency backup to kick start the hybrid powertrain if the 12v battery gets accidently flattened by whatever. Also I can confirm from other posts out there that a failing 12v battery will intermittantly give you a yellow warning triangle on the main dash reporting 'there is a problem with the powertrain system - please restart etc', and thanks to all on this forum who reported the alarm going off for no obvious reason - I definetly concur that leaving anything metal in the coutesy light compartment will set it off. Thankyou.

 

Be careful it doesn't eat a hole in your car with acid fumes, as under-hood flooded batteries sometimes do in non-hybrid cars.

I also deviated from the prescribed course in choosing a new 12V battery, but not to that extreme. I bought a common "U1" size 35 AH AGM deep-cycle battery, which are available from various sources on-line for about $65 and up. It wasn't difficult to vent it through the original vent hose (probably not necessary, but just to be extra-safe ... ), find suitable spacers, and make the existing terminal clamps work. So far, so good, after 3 months. It's only three-fourths the weight of the OE battery, well over three-fourths the capacity, and less than half the cost. I'll see how long it lasts.

 

The fumes are hydrogen, not "acid fumes". But hey:



This guy's known for acid fumes:

 

Yes, the fumes are theoretically just hydrogen and oxygen. However, some conventional car batteries have a nasty habit of surrounding themselves with corrosive acidic mess, especially after they're a couple of years old. Is that from acid (electrolyte) mist entrained in the gases, or from what? I've never seen or heard a good explanation why that happens, why some brands are so much worse than others, or what the ugly white and green gunk is comprised of.