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Prius critical design flaw kills batteries worse than Boeing 737 MAX MCAS issues

I drove a Toyota Corolla 2003 for over 15 years and past 210k miles and never had a problem. Now this brand new Prius is crapping out on me for no reason left and right and at the most inconvinent times. Seems like there is a software bug or firmware flaw somewhere in the actual car itself where it will wake itself up in the middle of the night for no reason, and without driver intervention, and proceed to discharge all the juice in the auxilary battery and then it refuses the start up because the aux/small battery is dead. This happened to me when I went to the nearby Kroger just like a mile or two away, parked and went to grab something to eat, took no more than ten minutes, and when I came back out the Prius completely died and wouldn’t start again. I had two other individuals with me as passengers that can attest to that I didn’t leave lights on and that indeed shutdown correctly. I took the Toyota dealership and they did a test and said nothing was wrong and that I must have left the engine on etc etc etc… So now I have dashcamera that records for a good minute or so after the engine is shutdown and car is powered off. I have since caught the car doing this many times even though I shutdown the engine correctly. And the only way to get it back again is to jump it, but the battery isn’t in the front, it is located in the back passenger right seat and almost impossible to reach and the only way to jump it is to have to mess with some capacitor panels/ fuse box in order to get it to the point where one can proceed with jumping it.

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Even though this is a Prius and literally half the car is a big battery, Toyota confirmed that the main power cannot be used to start a car and that if the car thinks the smaller aux battery is gone or too low, it won’t start the car regardless. In many of these instances my Prius still had full main batter power, way more than enough to start the car but due to the way it was designed that power could not be used for starting an hybrid electric car. Go figure…

I had the car died on me again just last night, here are two dashcam car video clips, the first one is from my return trip coming home from Kroger last night, notice that the video camera keeps recording for about 60 seconds after the engine is turned off. Notice that I remembered to switch off all car lights, and that the engine was shutdown before I went inside the home, and there were no beeps, no alarms and no warnings that would have otherwise been indictive of the engine being left on or the car did not shutdown /poweroff correctly etc…

The second clip is from this morning, notice the low noise immediately coming from the car when I tried to start it. There was enough battery to power the dashcam recorder but obviously not enough power to start the car engine… The low groaning noise is very indictive of a power failure or that the battery failed to keep power…

This is either a auxiliary battery (not main battery) issue, or a larger issue with the way Prius is designed. On some occasions I noticed the Prius car will WAKE itself up in the middle of the night for no reasons, seemingly to discharge battery/power and then shut itself down… it could be possible that the car is waking itself up but then on occassion it will fail to automatically return back to sleep and this bug/flaw may also be what is contributing to this strange but now chronic issue… It seems to be a defect in the very design of the Prius C itself and a manufacterur defect that Toyota must admit to, must fix and must resolve.

Word of advice, stay far far away from the Prius!!! The gas savings is not worth the trouble of getting killed because your cars randomly dies on the middle of the highway or refuses to start in an emergency situation!!!

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That kind of thinking won’t get anyone closer to a solution.

Complicated car, complicated design, complicated problems. Welcome to the world of Hybrids. Sorry about your problems.

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Since your current Toyota dealer can’t get a handle on this, I suggest you start keeping extremely detailed records of any and all interactions with anybody you had contact with at the dealership

Names, times, receipts, repair orders, etc.

Then you should think about contacting another Toyota dealer and explaining that you expect the problem to be resolved, because your car is under warranty.

Again, keep meticulous records

Lastly, you could consider contacting the regional manager, zone rep or whatever that position is referred to nowadays. He has the authority to light a fire under somebody’s . . . you get the idea

Even though it’s too soon in the process . . . start researching lemon law regulations in your state


I’m sure you are frustrated by this situation, but it’s not helpful to take it personally. The car doesn’t hate you. It’s a complex machine, and yours isn’t working right, but it’s not doing things"to you". It doesn’t care about you at all.

I have two thoughts. One is to be sure the keyless remote is far from the car whenever you are not driving. Having a remote near the car can run down a battery.

The other idea is to call Toyota regional office. The info on that should be in your owner’s manual. And keep notes as you go with everyone.

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What year and what model? I did a quick search at, and didn’t find any complaints like yours. You might search there as well, and also do a web search for similar complaints. You might also look at

OP infers it is a 2018 or 2019. Model is Prius C.

Infers, yes. But is it brand new, OP? If it is, do as the others said: keep records, elevate to Corporate, ask for a loaner. Does it have ANY aftermarket electronics, like a remote starter or alarm?

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So it is the 12v battery that is discharging? Sometimes a new 12v battery can have a factory defect that causes an intermittent internal short circuit. The battery will soon fail completely but because the fault is intermittent, it won’t be detected until it fails completely. I’m kinda surprised the dealer didn’t go ahead and just replace the battery, at least they should on the second visit.

As for jump starting the dead battery, check your owners manual for alternate battery terminals. Often when the battery is remotely located, there will be a box under the hood with a flip cap that has the alternate terminals in it for jump starting.

My hybrid wouldn’t jump start with a bad battery. You’d think getting 12v to the electronics would have worked, but only a new battery solved the problem.

I think it’s the 12 volt battery is what gets things going, so that’s probably what is failing or discharging
for some reason. OP might want to secure a copy of tsb 0195-17 about suggested battery maintenance. Googling shows how to access the battery, and it is indeed a little inconvenient, located up under the seat. But, what a 5-10 minute job to get at it? Not that serious of an issue, but could be frustrating when trying to do it at night in the cold, even worse, raining. Just keep the proper nylon pry-tool on hand needed to remove the clip is about the best you can do.

I doubt this is a design flaw. Probably a sample defect, a problem affecting OP’s particular Prius. This sort of problem is figured out the same for a Prius C as w/any other car, i.e. measure the battery drain when everything is off. Eventually you’ll catch it draining faster than it should (normal everything-off-drain is 50-100 mA or less), then it is just a matter of pulling fuses until the circuit that’s doing it is discovered. It’s also possible the battery itself is the problem, some kind of internal intermittent faulty. Maybe one of the crew building the car or even at the battery plant itself accidentally dropped the battery, still appeared to work so they shipped/installed it anyway, who knows.

Some other ideas

  • Install another 12v battery, might get lucky.
  • Load test the existing battery
  • Ask the dealership to keep the car for a few weeks and have one of their techs drive it as their daily driver, eventually it will fail and the tech should be able to debug the problem then. Ask them to give you a loaner car in the meantime.