# Question about Prius batteries **URL:** \ **Category:** Factual Questions\ **Created:** [November 11, 2021, 5:19pm UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196 "2021-11-11T17:19:50Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [November 12, 2021, 4:45am UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/21 "2021-11-12T04:45:30Z")
I got a Big Red Triangle on my 2005 Prius a couple of years ago. One of the cells in one of the modules of the battery pack failed. I found a [local place](https://www.unlimitedservice.us/) that replaced the module for half of what the Toyota dealership would have charged. My '99 Jeep Cherokee, which I bought new, seems to have battery issues. It’s seldom driven, and I suspect there’s a ‘leak’ in the electrical system. It starts reliably, but dashboard turn signal indicators don’t work and sometimes the central door locks don’t work. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [November 12, 2021, 11:35am UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/22 "2021-11-12T11:35:47Z")
> [@Cartooniverse](#): > > This car went unstarted and undriven from late Jan to roughly August of this year. That’s a long time for a car battery to sit in a car without being charged. Even when not explicitly powered up, modern cars have security systems, clocks, remote access systems and other gadgets that slowly suck the life out of a battery. add in some age, and maybe some accumulated crud that’s developed a weakly conductive path on the exterior of the battery between the two terminals, and I’m not surprised it’s unable to start after 8 months. How old is that battery (the standard 12V, not the drivetrain battery)? I highly recommend a Battery Tender: [https://www.amazon.com/gp/product/B07XMJDJX7](https://www.amazon.com/gp/product/B07XMJDJX7) This is what gets my motorcycle through the winter and assures a healthy start for the first ride of the spring. Last year I bought another one because my wife stopped driving when the pandemic started (though I still try to drive her car every few weeks to move the tires and burn some of the old gas). ---
**Author:** ![GaryM](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/garym/32/241_2.png) [@GaryM](https://boards.straightdope.com/u/GaryM)\ **Post date:** [November 13, 2021, 12:06am UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/23 "2021-11-13T00:06:38Z")
I use Battery Tender models by the same company on my tractor and mower over the winter. They work well, though not really capable of recharging a dead battery. The unit linked is a charger that appears to be a tender as well. ---
**Author:** ![Ziberian](https://avatars.discourse-cdn.com/v4/letter/z/919ad9/32.png) [@Ziberian](https://boards.straightdope.com/u/Ziberian)\ **Post date:** [November 13, 2021, 2:28am UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/24 "2021-11-13T02:28:19Z")
> [@Johnny\_L.A](#): > > but dashboard turn signal indicators don’t work and sometimes the central door locks don’t work. Could this be a fuse gone bad? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [November 13, 2021, 2:34am UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/25 "2021-11-13T02:34:56Z")
No, fuses are never intermittent. Well, hardly ever. These sort of intermittent problems are often due to bad ground connections. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [November 13, 2021, 2:48pm UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/26 "2021-11-13T14:48:56Z")
It’s been suggested that I pull all of the fuses and clean the contacts, but I haven’t done it yet. As I said, the Jeep doesn’t get driven much. After sitting, the pattern is this: The left turn signal indicator on the dashboard stops flashing. Next, the right dashboard indicator stops flashing. The turn signals themselves do work. Then, the central door locks stop working. I’ll thumb the fob as I approach, and I don’t hear the familiar ‘clunk’ of the doors unlocking. I use the key to open the door, and the central lock switch has no effect (lest you think it’s a weak battery in the fob). Drive the jeep a little bit, and you get the door locks back; but it’s been months since the dashboard indicators… erm, indicated. I suppose it could be a ground issue, but I don’t know why it would affect certain things in a certain order. As I said, I suspect there is a ‘leak’ in the electrical system (as opposed to just the normal drain of the clock, etc.). I need to take it into the dealer to have them do diagnostics. But this is a thread about Prius batteries. No battery problems since the failed cell in the module, and I have no idea how old the 12 v battery is. But it is getting a new set of tires Monday afternoon. ---
**Author:** ![Precambrianmollusc](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/precambrianmollusc/32/63_2.png) [@Precambrianmollusc](https://boards.straightdope.com/u/Precambrianmollusc)\ **Post date:** [November 16, 2021, 3:17am UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/27 "2021-11-16T03:17:07Z")
The OPs 12v auxiliary battery is an absorbent glass matt battery and is original ( unless I misunderstood that parr) from 2003 so 17 or 18 years old, which is pretty good going for a battery so its not surprising that it is not holding a charge. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [November 16, 2021, 11:36am UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/28 "2021-11-16T11:36:36Z")
> [@Precambrianmollusc](#): > > The OPs 12v auxiliary battery is an absorbent glass matt battery and is original ( unless I misunderstood that parr) from 2003 so 17 or 18 years old, which is pretty good going for a battery so its not surprising that it is not holding a charge. I think in the OP @Cartooniverse was referring to the large propulsion battery being 17-18 years old, not the standard automotive 12-volt battery: > [@Cartooniverse](#): > > The car is from 2003. Original battery pack. Dealer confirms that several in the pack are failing. For reasons not worth going into, the car will remain in Mom’s driveway. It DOES drive. She is no longer driving it. > > Here’s the problem. The car won’t start unless it’s driven every day. The normal battery ( located in the left side of the trunk ) will take a charge from an external charger and the car will start and drive fine. Since we are only at Mom’s every few weeks, the normal battery is always dead. AIUI, “original battery pack” here refers to the large propulsion battery, and “normal battery (located in the left side of the trunk)” refers to the standard 12-volt automotive battery, the age of which isn’t clearly indicated. 17-18 years is an awful long time for one of those to be in service; 5 years is much more typical. ---
**Author:** ![Precambrianmollusc](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/precambrianmollusc/32/63_2.png) [@Precambrianmollusc](https://boards.straightdope.com/u/Precambrianmollusc)\ **Post date:** [November 16, 2021, 2:18pm UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/29 "2021-11-16T14:18:37Z")
Yeah could be, I guess it is not specified as the to the age of the auxiliary battery, and 18 would be probably way to old for it not to have been replaced before, but it if is the original , it has had an awesome run! ---
**Author:** ![Cartooniverse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cartooniverse/32/3084_2.png) [@Cartooniverse](https://boards.straightdope.com/u/Cartooniverse)\ **Post date:** [November 16, 2021, 2:45pm UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/30 "2021-11-16T14:45:32Z")
Good points. I believe the car battery is less than 7 years old. The Propulsion battery pack is original. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [November 16, 2021, 6:45pm UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/31 "2021-11-16T18:45:55Z")
> [@Cartooniverse](#): > > Good points. I believe the car battery is less than 7 years old. If it’s as much as 7 years old, that’s pushing it. It wouldn’t be surprising if it had developed an internal short in one or more of the cells by this time, preventing it from holding adequate charge for an acceptably long time. ---
**Author:** ![SenorBeef](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senorbeef/32/2220_2.png) [@SenorBeef](https://boards.straightdope.com/u/SenorBeef)\ **Post date:** [November 16, 2021, 6:51pm UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/32 "2021-11-16T18:51:00Z")
Is it standard for hybrids to have standard 12v batteries in addition to the main hybrid battery? Is it just a matter of amperage to run the starter? It seems like it’d be more efficient to just have one battery. On the other hand, hybrids start and stop their motors all the time - maybe the wear of the starting process is passed onto the replaceable standard battery? ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [November 16, 2021, 7:15pm UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/33 "2021-11-16T19:15:15Z")
I linked upthread to a story about a _Tesla_ that had a failed 12V auto battery and Googling, Nissan Leafs also have 12V batteries. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [November 16, 2021, 7:15pm UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/34 "2021-11-16T19:15:18Z")
The “propulsion” battery is much higher voltage. Using it for starting and running all the accessories would entail an enormous and expensive DC-DC converter to step down the high voltage to 12V. ---
**Author:** ![SenorBeef](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senorbeef/32/2220_2.png) [@SenorBeef](https://boards.straightdope.com/u/SenorBeef)\ **Post date:** [November 16, 2021, 7:18pm UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/35 "2021-11-16T19:18:33Z")
Aha. I didn’t realize that voltage stepdowns were so expensive. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [November 16, 2021, 8:55pm UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/36 "2021-11-16T20:55:23Z")
They are only expensive when they need to provide 100A or more, for the starter. ---
**Author:** ![N9IWP](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/n9iwp/32/3154_2.png) [@N9IWP](https://boards.straightdope.com/u/N9IWP)\ **Post date:** [November 16, 2021, 10:55pm UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/37 "2021-11-16T22:55:11Z")
In a Prius the 12v battery just powers the computer and dome lights and such IIRC. I am almost positive it does not start the gas engine. Brian ---
**Author:** ![SenorBeef](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senorbeef/32/2220_2.png) [@SenorBeef](https://boards.straightdope.com/u/SenorBeef)\ **Post date:** [November 16, 2021, 11:32pm UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/38 "2021-11-16T23:32:14Z")
That makes more sense to me, since the engine starter can be designed around running at high voltage, rather than running the starter off the 12v battery or downconverting the high voltage. Plus you’re less likely to be left in a situation where the car can’t start due to a dead battery from non-use, since the hybrid battery can store more energy than the chemical one. ---
**Author:** ![Voyager](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voyager/32/133_2.png) [@Voyager](https://boards.straightdope.com/u/Voyager)\ **Post date:** [November 17, 2021, 2:50am UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/39 "2021-11-17T02:50:22Z")
> [@N9IWP](#): > > In a Prius the 12v battery just powers the computer and dome lights and such IIRC. I am almost positive it does not start the gas engine. I don’t know, but when my battery was dead the engine didn’t start until it got jumped, just like in a regular car. ---
**Author:** ![N9IWP](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/n9iwp/32/3154_2.png) [@N9IWP](https://boards.straightdope.com/u/N9IWP)\ **Post date:** [November 17, 2021, 3:13am UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/40 "2021-11-17T03:13:17Z")
The 12v battery is need to close the relay for the high voltage battery – so the HV system is disconnected from everything when the car isn’t running. Brian [Previous page](https://boards.straightdope.com/t/question-about-prius-batteries/954196.md?page=1) [Next page](https://boards.straightdope.com/t/question-about-prius-batteries/954196.md?page=3)