# 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:** 8\ **Page:** 3
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [November 17, 2021, 4:46am UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/41 "2021-11-17T04:46:56Z")
> [@Cartooniverse](#): > > Here’s my idea: Put a switch in line in the + side of the normal battery. Bear in mind that this would need to be a hellava switch. They do exist, but it would need to be able to cope with several hundred amps. Not your average switch. ---
**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 17, 2021, 1:43pm UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/42 "2021-11-17T13:43:11Z")
Like [this](https://www.amazon.com/Ampper-Battery-Disconnect-Isolator-Vehicle/dp/B07413JWLD/ref=sr_1_4?keywords=battery%2Bdisconnect%2Bswitch&qid=1637156523&s=automotive&sr=1-4&th=1) one? ---
**Author:** ![Driver8](https://avatars.discourse-cdn.com/v4/letter/d/b5a626/32.png) [@Driver8](https://boards.straightdope.com/u/Driver8)\ **Post date:** [November 17, 2021, 5:51pm UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/43 "2021-11-17T17:51:22Z")
> [@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 think this is true in the ICE / battery hybrid Prius. I believe the engine start uses the 12V battery, same as a normal gas car. That’s consistent with our experience when that battery needs to be jump started. I’m not even sure if the drivetrain battery is even necessary for normal operations. I suspect the car will still work even if it’s completely bust or discharged; just with compromised gas mileage. ---
**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, 6:17pm UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/44 "2021-11-17T18:17:06Z")
Links that support my position that only the HV battery is sues to start the ICE: > **[Specializing in: dictionaries including the Collins Cobuild, Oxford English...](https://store.e-learn-aid.com/)** > > Large collection of English Dictionaries on CD, Bilingual Dictionaries, Study Skills books(Understanding Improvement), English as a Second Language dictionaries, Grammar books, Palm Pilot Dictionaries, Business Management books > **[What exactly is the 12V battery used for?](https://priuschat.com/threads/what-exactly-is-the-12v-battery-used-for.73728/)** > > The battery in the trunk: What is it used for? > > If it goes dead, and I get a jump start, how do I ensure that the ICE is run long enough to charge up... > **[Why do hybrid vehicles have two batteries?](https://www.linkedin.com/pulse/why-do-hybrid-vehicles-have-two-batteries-timothy-livingston)** > > Most hybrid vehicles, like the Toyota Prius, have two batteries. A smaller 12 Volt auxiliary battery, and the much larger high voltage Hybrid System Battery. Wish I could find something definitive from toyota Brian ---
**Author:** ![tullsterx](https://avatars.discourse-cdn.com/v4/letter/t/e9bcb4/32.png) [@tullsterx](https://boards.straightdope.com/u/tullsterx)\ **Post date:** [November 18, 2021, 1:43pm UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/45 "2021-11-18T13:43:09Z")
You should take the car to Auto Zone or some place and get the battery tested. It’s not uncommon at all in my experience for car batteries to “go bad.” I think every car I’ve ever had I’ve had to replace the battery at least once. ---
**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 22, 2021, 7:33pm UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/46 "2021-11-22T19:33:17Z")
Update: The car was driven for a total of perhaps 60 Minutes last Monday. It’s sat until Friday. My brother was able to get in start the car and drive around with zero problem. At this point I am guessing that it simply needs to be driven enough for her car battery to maintain a decent charge. Kind of the simplest solution. I agree with the last post however it is worth pulling that battery and having it analyzed. There is an AutoZone close to Mom’s house and I will do that next time I’m there. Thank you for the great idea! ---
**Author:** ![hibernicus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hibernicus/32/2802_2.png) [@hibernicus](https://boards.straightdope.com/u/hibernicus)\ **Post date:** [November 22, 2021, 9:37pm UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/47 "2021-11-22T21:37:13Z")
I have a 2009 Prius, which is driven relatively rarely. I have had problems over the years with the 12V battery discharging. I have solved this problem by buying a [solar-powered battery maintainer](https://www.amazon.co.uk/Powered-Battery-Charger-Caravan-Package/dp/B07P7C6QLD/) - basically a 5W solar panel that sits on the dash and trickle charges the battery via the OBD2 port. As pointed out above, the 12V battery is only required to activate the car’s electronic control systems; it is not used to start the engine. One other thing: check that the battery isn’t sitting in a puddle of water. If the seals around the rear lights become defective, allowing rainwater to enter the trunk area, the water can accumulate in the battery compartment. ---
**Author:** ![Satchmo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/satchmo/32/4223_2.png) [@Satchmo](https://boards.straightdope.com/u/Satchmo)\ **Post date:** [December 12, 2021, 7:42pm UTC](https://boards.straightdope.com/t/question-about-prius-batteries/954196/48 "2021-12-12T19:42:29Z")
I have a 2010 Prius, it has a metal plate covering where the starter would go into the engine. My mechanic says that they use that same engine in other types of vehicles, but on the Prius, the Big batteries just start the engine directly. [Previous page](https://boards.straightdope.com/t/question-about-prius-batteries/954196.md?page=2)