Prius turn on and off repeatedly!!!

I just had something really weird happen to me today. I went out to roll up the windows and move my Prius. Everything was fine at first. I pushed power and rolled up the windows. I then hit power again and turned the car off. Everything was normal.

However I decided to move the car about 15 seconds later and the car wouldn't power up. The MFD just started rapidly blinking the start-up screen and all the warning lights came on. I tried to turn the car off but pushing the button didn't do anything. I then inserted the key fob and the car powered down when I hit the power button. (The car flashed the start-up screen for ~ 30 seconds)

I then attempted to start the car again and again it wouldn't start and went into a continuous loop of powering on then off. This time it was a longer cycle of about 3-5 seconds and the A/C powered up in the cycle. I again tried to turn the car off but pushing the button had no effect. I tried to remove the fob but it wouldn't come out until I turn off SKS by pushing the button on the lower dash. Then the car powered down.

I attempted to start the car a third time and it powered up like normal. I drove around the block and parked it with no problems.

Any idea what would case the car to go into a continuous loop of powering on and off? (No, I didn't push the power button multiple times)

 

Thanks for the testing procedure, I'll check battery voltage tonight. The car did start up like normal this morning when my wife went to work.


Some questions on battery replacements:
How much is a stock Toyota battery? $168 for the optima kit (now reduced to $138) is about twice what I expect to pay for a battery.

I also see that Auto Zone stocks the following battery for the Prius:
Duralast 51R-DLG
27.7 lb
500 Cold Cranking Amps
650 Cranking Amps
8 year warranty with free replacement for the first 3 years
$89.99

That seems to be a more reasonable price for a battery.

 

I'll do that. The description says that it vents to the outside.

 

According the the diagnostic test the battery is dead. When I first went into the diagnostic screen the voltage was 11.5. This dropped to 10V when I hit power then up to 14.2V when I hit power again. So it seems the battery is dead and the car is cooking the battery trying to charge it.

I'll explore my options a bit more next week. Right now I'm getting ready for a 5 day motorcycle trip. I'm just happy to know that nothing is wrong with the car.

 

I decided to simply purchase the Optima battery and installation kit recommended above. I decided on the Optima because:

• Optima's have a good reputation on EV forums
• $138 for an Optima is a great deal
• I know it will fit as others have used it
• With tax + core charge the Duralast cost $115

(I bought a motorcycle without a battery. When I buy a battery for it I will have to pay a core charge. Instead I will simply exchange the Prius battery to avoid the $15 core charge)

 

The Optima battery installed quite easily, it only took about 45 minutes and that includes removing the fuse box and positive cable and repositioning it. (The sketch shows in installed one way while the photograph has it installed the opposite way.)

However, now I'm concerned that the battery wasn't the problem. After I removed the stock battery I checked voltage and put it on my battery charger. When the battery came out of the car it measured at 12.2 V but after about 3 hours on the charger (battery tender trickle charger) the charger turned off and showed the battery was charged. Sure enough the voltage measured 13.8 volts. That is a little low for a new battery but still pretty good. I'll have to check it with a load to be certain. I've had batteries in the past that show good voltage but still are bad.

 

That is where I purchased my kit. They have dropped the price from $239 to $163. Optima is also offering a $25 factory rebate so that dropped the price to $138. No tax and free shipping. (I was amazed they managed to fit the battery and kit into a USPS flat rate box!)

I charged the Optima battery with my battery charger before I installed it in the car. I have no worries about the Optima battery.

I am worried about the charging system in my Prius. When I removed the stock battery from my car it was dead (12.2 volts). However, just for grins, I hooked up the stock Toyota battery to my battery charger just to see what it would do. Usually a dead battery will charge and charge for hours but will never rise in voltage. That is not what happened. Instead the stock battery showed fully charged after 3 hours. That makes me believe that my problem is not a bad battery but instead a problem with the charging system in my Prius.

I didn’t have much time last night to experiment but I did hook up my inverter to the stock Toyota battery to see if it would power a load. It would run the inverter’s fan and a 100W light bulb but the voltage sagged from 12.9V down to 12.3V. It would not run my circular saw but neither would the fully charged and functional battery in my motorcycle. The circular saw says 120V / 0.9 amps but it drew enough amps to blow the 10 amp fuse in my multimeter. That was the end of my experiment.

Tonight I will hook the stock Toyota battery up to my motorcycle and see if it will crank.

 

I'm pretty confident that the old battery was ready for replacement. When I hooked it up to my smallest motorcycle (250cc single) it would just barely turn it over. (It would turn one revolution then stop) When I hooked it up to my 440cc twin it wouldn't even turn over the engine but instead the relay only clicked. This was with the battery coming straight off the charger.

I may do that this weekend. Last night I checked the Optima with the MDF. It was 12.8V at first then jumped to 13.8V in the ready mode.