Prius with bad traction battery

Nope. (Well, probably not.) The traction battery is what starts the ICE. If it's not working, there's no way to start the ICE. Even if it will start the ICE it will run extremely poorly if at all depending on how bad the battery is. There are faults that will let it limp, but you never know when it'll just stop.

 

First, the 12v battery needs to be good enough to boot all the computers when you press the power button, along with running the abs pump for a few moments. The abs pump will kill a very weak 12v battery and may prevent the car from starting properly. Once the computers boot and all is good, the main contactors in the HV battery will close and put the car to ready condition, where the DC/DC takes over from the 12v battery, similar to how an alternator does in an ICE car. A few seconds later, the HV battery will spin the transaxle, attempting to start the engine for warmup. Depending on the condition of the HV battery, the car may not even go to ready. If it's just a weak module or two, the battery will likely still let the car go to ready condition and try to start the engine. IF so, then you should be able to drive it. If the only code is a P0A80, the car will drive normally. If there's a P0A80 and a P30xx to designate a specific block that is weak, the car will be in limp mode. Driveable, but very little power. If you're not concerned with maintaining the codes in memory, all codes can be reset by disconnecting the 12v battery for a few moments. The ecus will return to default values. The default value for the HV battery is mid-range SOC, so this 'reset' will often let a weak HV battery make one more try to start the engine before the car realizes the SOC of the HV battery is actually too low.

 

State of Charge.

If the owner says it starts and drives, then it should be good to go with just a new 12v. For how long? who knows....but if the engine is actually starting, then the HV battery must be good enough to fire it up. With a dead 12v, and living only with a jump start, any codes would be reset every time the car is turned off. That's likely why no codes are showing up yet. Car isn't being run long enough for problems to be recognized.

 

If I was in your situation and I got this one the first thing I'd do is charge and balance the pack with a high voltage trickle charger... After sitting for a couple years each module will self-discharge at a slightly different rate and need charging and balancing and contrary to what others say above, I've had lots of luck with reviving packs that have been sitting for years. They're way easier to rebuild than battery packs that people kept trying to drive with all the warning lights on.

 

You can bring a scanner and drive it as far as you want. Just about every one I've driven with a bad hybrid battery still drives the same.

1 or 2 were so bad you would have no power and it could not be driven. But, the trick to bypass that is to just have a scanner connected to OBD port and delete the code whenever it comes up. That makes it go from barely limping home with zero power and non-drivable to being able to go 90mph on the freeway. Delete code.

(That is my experience driving them on bad batteries. YMMV and I am not a mechanic.)

EDIT: Most I have driven is 45 minutes to a mechanic on 2 or even 3 occasions but I obviously wouldn't advise going much over that length of time.

 

It used to be that we'd just send everyone to @jeff652 and have him sell you $700 of gear via his hybridautomotive.com website but I think he mostly abandoned his business as items returned for repair take many months to process, their quality control has gone from bad to worse and he was last seen on PriusChat in February and the year before was on here three times.

His competition at Maxx Volts Hybrid Automotive Grid Charger Reconditioning Systems however make much higher quality battery maintenance gear at a better price and if you want to DIY it super simple like you can follow our efforts here: Build Hybrid Battery Maintenance Gear For Under $100 | PriusChat

 

Sometimes when I'm diagnosing an especially crappy battery I'll as much as 3 or 4 times a day clear the warning lights and get it out of limp mode in less than 30 seconds while driving... Key is to keep an eye on battery temp because if it gets too hot you can't keep driving without causing damage.

 

what temp is ‘too hot’?

 

If you are replacing battery then who cares....And if the battery is so completely shot and old then I don't think you want to slap a couple $10 Chinese made cells in it and call it "rebuilt". Best bet get one brand new for about $1600 or go on car-part.com and get one USED (OEM) with about 120-140k miles for $500-$600

 

PriusCamper said: ↑
Sometimes when I'm diagnosing an especially crappy battery I'll as much as 3 or 4 times a day clear the warning lights and get it out of limp mode in less than 30 seconds while driving... Key is to keep an eye on battery temp because if it gets too hot you can't keep driving without causing damage.

So I asked, "what temp is ‘too hot’?"

 

It depends... But in general once you get over 100 degrees fahrenheit you're getting close to the limit. But of course if you live in a place where its 95 degrees out than that 100' temp is not so hot. Perhaps 120 degrees is the extreme upper limit, but again its relative to the ambient temp your vehicle lives in.