Low mileage driver. Will that harm a Prius?

No. It's too tightly integrated, part 'n parcel.

 

I Agree with Mendel, the traction battery is needed to start the Internal Combustion Engine (ICE). The 12v battery is only used to run accessories and power the electronics until the Inverter (powered from the traction battery) starts up and powers the 12v bus.

JeffD

 

I recall too: when you first start up, even with the engine running at fast-idle, it's virtually all-electric propulsion. And whenever you're in reverse, it's also all-electric propulsion, it's not technically possible with the transaxle to reverse using engine propulsion.

 

I do not think it is possible to move the parking pawl without the HV battery either.

 

While old Honda IMA systems (Insight, Civic Hybrid) could drive without the traction battery, Toyota HSD systems cannot.

 

Yes and no.

Yes, the car can still be driven if the pack has failed but not if it's completely shorted; however, the ICE isn't designed to provide enough power, especially acceleration, and the vehicle will operate in "turtle mode". No, it can't be driven at all with the pack removed; it needs the pack to start the ICE.

 

Low mileage won't be a problem if you are still driving it very often. If your driving habits leave the car unused for weeks or months at a time, the hybrid battery won't like it. For example, I have family members that live in Vancouver for 4-5 months during the spring and summer. But they move somewhere warmer during the rainy season, while leaving their car in unused Vancouver. This would be a bad set up for a hybrid.

 

Don't you mean the little 12V battery, not the hybrid battery?

The 12V is a weak point on the Prius family. The hybrid batteries are more robust, at least through Gen3.

 

From what I've read about Traction Batteries, while sometimes they "give out" - many fade gradually - like your laptop or smartphone battery, where it will last less and less time.

It will become less and less effective, limping slightly - but if it gives up the ghost entirely, you don't go anywhere.

There are several reports on Google and PriusChat of owners who knew their battery was gradually failing, bought a new Traction battery and it felt like a brand-new car again.

 

If you live in a hot climate (or have poor cooling air), all of your modules will age rapidly (the inner ones in the stack will age faster due to poorer cooling in a gen2). My 2004 Prius HV battery exhibited the other failure mode (I live in a temperate climate - CT). At 195k miles (about 8 years of use) one cell in one module had drifted to a lower state of charge (SOC) than the rest. When the HV battery was discharged to its lowest value, that cell was reversed which made it a permanent short circuit and that module's voltage dropped by 1.2 volts causing the expected Christmas tree lights on the displays. This failure mode can be prevented (at least delayed) by periodically balancing (the process of getting lower cell SOC up to that of the stronger cells) your HV battery.

The remaining 27 modules were still usable (at only a somewhat reduced capacity) and were used by 6 other Prius owners to "refurbish" their HV batteries.

JeffD

 

My 2006 Gen 2 traction battery failed at 71,000 miles (and five years) when I was about ten miles from home. I was able to drive it home just on ICE, although I had to stay on surface streets because it was extremely underpowered. I could coax it up to 45 but acceleration was incredibly anemic, especially off the line as it had very little torque starting from standstill. I'm sure I made a few people behind me mad who probably assumed I was hypermiling . The next morning I didn't know if it would start, but it did and I was able to drive it to the dealer. Same incredibly anemic power so it was clearly running just on ICE. The dealer said the hybrid battery needed to be replaced, which they did under warranty . Although I wasn't exactly thrilled that the battery died, I suddenly had a brand new traction battery for free at 71,000 miles! The car is now at 145,000 but my traction battery is only 75,000 miles and seven years old.

So the next question is, how was I able to drive and start the engine? Maybe the traction battery still had some power but the computer was refusing to allow it to be used for torque, and only allowing it to be used for accessories and engine starting. Either that or the accessories and engine starting was provided by the 12V, which presumably in that case was being kept charged by ICE. However that would mean that Toyota built in that capability as a failsafe for situations where the traction battery is dead so that you can still drive. Whether or not it has that capability or not I have no idea.

 

The ICE was already running so you could drive home in "limp" mode. If the traction battery is completely dead it cannot spin the ICE to start it and you have a lawn ornament, not a car.

JeffD

 

It most likely had the common P0A80 fault which sends the car into protection mode that you experienced. BTDT The battery isn't completely dead or completely shorted so the software still allows it to start the ICE but then is kicked out of the party after that (ICE only). Same thing happens if the battery gets too hot. We just saw a thread here about a brand new Toyota battery and the duct work was incorrectly installed causing the car to light up the dash and go into turtle mode. Bottom line is the software tries to protect the battery at all costs.

 

Since the car started the next morning then apparently my first theory was correct, the computer allowed the traction battery to start ICE but due to whatever problem the battery had the computer would not use it for torque. Although I don't know what provided 12V during the drive home and the drive to the dealer the next day. Maybe if the traction battery seems up to it the computer will allow it to recharge the 12V battery. If not, then another possibility is that in these situations ICE can provide 12V power. Although I tend to doubt it because that would require additional circuitry, which I don't think Toyota would put in for what they would see as a rare situation. The only other possibility is that for those few miles that I drove in this condition the 12V battery was supplying electrical power, and if it had died before I got to the dealer I would have been stranded. The 12V was just over one year old at that time so probably would have been up to it. Either way it apparently wasn't harmed as the 12V lasted another six years after that.

 

MG1 should be able to power the high voltage bus, allowing HV->12V inverter to provide all the needed 12V.

If the high voltage battery has enough oomph to start the ICE, then it ought to be an adequate buffer on that voltage bus, even if it can no longer handle actual propulsion.

Not directly, but only through that MG1 -> HV bus -> inverter path mentioned above.

 

Interesting. The Traction Battery would likely have had enough reserve left to keep the 12V charged to run the computer etc, plus start the ICE. You may not have been aware of it, but it may have been doing some limited driving too - hard to tell.

Did you notice any issues with brakes or steering - and a/c - which I think (?) are driven by the traction battery.

When my Smartphone was playing up recently with an almost dead battery, I tested the battery voltage after charging and it was about the same as the new battery I'd just bought. But, with the "load" of the phone, it would only last 6 or 7 hours idle, or ½ - 1 hr of actually "working".

 

Alan,

In "limp" mode (AKA Turtle), the AC is disabled to reduce the load on the weakened traction battery.

JeffD