Early Indication of Battery Failure?

It is normal. Battery is never fully charged until you have long downhill.

 

agreed. how many miles on her?

 

Interestingly enough, I'm now getting full green bars with much shorter downhill stints (maybe once a month) compared with when I bought the car in 2015 and then recall seeing full green once in the following two years on an extremely long and steep downhill. So full green showing up more often might indicate the battery is deteriorating.

 

newpriusbatteries.com

 

Yes, this mean capacity is getting lower so using normal charging regime it take less time to fully charge it. Battery ECU can limit power taken out or in to the battery but this mean battery is really dying or getting hot.

 

As stated, it almost never gets full on purpose. Its better for the battery and it keeps the regen braking functional, saving your hydraulic brakes and improving mileage.

The hv battery may be getting old when it self discharges overnight but it is not critical yet. A nine or ten year old battery (could have been made in fall 2011) is old. Cold weather on these high voltage battery is not bad. Heat is their enemy so they often fail sooner down south.

With that said, it is hard to say when the big hybrid triangle alarm light might come. It could easily be two or three years. I would start to research the options for that day. Do not consider used and be careful since many stretch the truth with their "refurb, reconditioned, remanufactured" marketing of used batteries. They don't last. New gets you eight or nine more years for a little more. Besides Toyota there is only one do it yourself (diy) new module aftermarket that is the same battery chemistry. Lithium options are likely to be widely available soon but are still diy.

The good news is the high voltage battery will almost never strand you even if the hybrid light comes on. In fact the hv battery is less concerning than other failures on these cars that are not battery related.

 

Sounds like normal behaviour to me. You can get an OBD II reader and an app called Dr. Prius to test the remaining life in your battery, though I've heard some people say it doesn't give very accurate results. At least I think if it was dead or close to dead you'd probably get some indication. I just bought a 2010 Prius and it tested to have 80% remaining life so that made me feel better!

Most people dont realize that the Prius battery is quite small, and is meant to charge and discharge fairly rapidly. If you are getting 45-55 MPG then your battery is not dead. What you described is probably how a brand new Prius battery works, and the car is smart enough to manage the battery so you dont need to worry much about it.