2007 Prius hybrid battery problem on a hot day

As hybrid batteries get older (use and time) they do deteriorate, especially in temperature extremes. The car will "deal with it" as best it can by adjusting the mix between gas/electric, running the battery fan near the back seat if battery gets hot etc. If there are no warming lights on the dash you are probably ok...for now at least.

How many miles on your car? In the US it's rare for batteries to fail before 150k miles (241k km's)

 

there's a fan that comes on inside the vent when the battery goes over a certain temp. you may want to clean the battery vent fan as some have found it clogged and not cooling the battery properly.

 

Have you ever cleaned your HV Battery Fan? It could be clogged. Please use instructions I provided some time ago, it may solve your problem!

Clean HV fan when changing 12 Volt | PriusChat

Also, have you checked your inverter pump by removing the cap from the inverter fluid holder? With the car in ready, remove the cap and check for turbulance. If not, your inverter could be over-heating and a replacement pump should be installed...

 

If car has 90k km's Hybrid system should still be under factory warranty. (what is the hybrid warranty in Oz?) Next time you go to the dealer have them "note your file" that you've noticed hybrid battery weirdness, that way if it ever fails there will be a paper trail.

 

You let the cabin get extremely hot while loading up. Cabin hot=Hybrid battery hot.

I don't let my car sit for a moment without the shade in the window. They sell the custom shade here at the PC SHOP. It fits tailor perfect and is insulated. Highly recommend it.

Then heavy load with car at full max ac with hot cabin. Then you demanded power from the car not realizing the Hybrid battery was in one pink. That power demand on a very low Hybrid battery will turn on the fan. This is all normal.

Your car goes into one pink all the time you just never noticed. Unless you never go through a drive through? Or sit in stop & go. Then in one pink it commands the car engine to turn on. You'll immed. notice you have poor gas pedal response as the Hybrid battery is putting a load on the Inverter and the Inverter is putting a load on the mg to charge the hybrid battery.

Not sure how hard you drive the car especially if it see's alot of hills but may be time for the full fluid tune-up. Change ICE coolant. Change the Inverter coolant. Replace trans fluid. Change motor oil.
Check water pump belt. Check water pump for weeping. These are all due at 100,000 miles but alot of us here do these at 50,000. Have to ask yourself how important is it to me to keep the car running at peak performance and not give me any headaches?

And check hybrid battery fan for clogging as mentioned. My 2007 hbf wasn't bad at all at 70,000 miles just a little dust on it. But I did remove the bearing dust sticker and lubed it.

 

how long have you owned it?

 

That's only about one more year, so please take heed of what people are telling you here and check that your rear battery fan is not clogged up.

I bought my Prius second hand in Sept 2009, and on the very first summer I started getting exactly the same symptoms as yourself, poor battery performance and sometimes loud battery fan in the back seat. I pulled the panels in the rear hatch to inspect the fan and it was totally clogged with dust and fur. After I cleaned it out my problems went away.

See my pictures here: Fur and dirt causing major battery problems | Page 2 | PriusChat

 

could be your 12v.

 

still a good idea to test it.