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2012 Toyota Prius battery fault

I own a 2012 Toyota Prius which was working fine, since last few months some warning light including Engine sign shows up which disappear after programming, Electrician referred to Hybrid battery fault which were opened, cleaned the terminals and load tested, final voltage after load tested with 12 Volt lamp (One minutes) were 7.8v. and consent. I obserevd some time delay in Engine starting.
Please advise what should be the reason and its remedy.
Thanks in advance

Are you asking about the 12V battery that starts the gas engine? If so sounds like you need a new battery… I’m surprised the battery is capable of starting your engine at all.

Thank you for your response, no I was referring to Hybrid batteries. Each of them was tested for 1mint with 12V Head lamp and voltage were 7.8.

Please advise.

Best regards,


Could you explain this in more detail, please. What is 1mint?

Thanks Russell, all 28 batteries were load tested with 12 volt head lamp for the duration of 1 minute and voltage remaind 7.8 volt. Pls advise.

Best regards

Somehow it does not sound like you are at a place that really knows what they are doing . I think you need to have a second opinion.

How old is the 12 volt battery?

Seems you are talking about two different things. As far as I can ascertain 7.8 volts is correct for each cell in the hybrid battery pack.
The not exactly clear what you mean “some time delay in engine starting”
Do you mean the gas engine is slow to start? Cranks slowly before starting? The gas engine is started by a separate 12 volt battery. That battery may be failing, was it tested?

It is genuine came with 2012 model Prius.

Best regards,


@cdaquila Not that anyone is going to call this person but you might use your magic eraser.

The gas engine is not started by the 12 volt battery. It is started by the main battery pack. However, a weak 12 volt battery will cause all kinds of problems because it powers much of the electronics. How old is the 12 volt battery?

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That is unclear, the car can be driven before the engine starts, are you experiencing a delay with the “Ready” display?

Nominal voltage for each battery module (6 cells) is 7.2 volts. What is the fault code that you are trying to address?

Thank you, I was making an assumption. So the 12V is there to power the electronics, ie radio, windows, locks, etc?

A genuine Toyota battery that came with a 2012 car could be near the end of its useful life. It’s not unusual for a 12V auto battery to have a lifespan of 5-6 years.

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Get the 12 volt battery tested if you can. Replace it if bad, or if you can’t get it tested, replace it anyway. That is probably the least expensive component to replace.

Yes, and the computers. That’s where a weak 12 volt battery causes real problems.