Early Indications of HV battery Weakness (@91k miles)

Firstly let me say that the car is still running perfectly and giving great MPG, but I just wanted to document some early signs of traction battery weakness and see if anyone else has notice these particular symptoms.

1. Descending hills I get up to the full 8 green bars much sooner than it used to do. When I first got the car (at about 40k miles) I rarely saw it top out the battery charge. It needed to descend about 80 meters (change in elevation) of fairly steep hills to go from the nominal six bars up to all eight green. Now it seems I can max it out with as little as about 45m change in elevation (if it's steep and taken slowly).

2. SOC anomalies after full 8 green charge. After topping out the battery to max charge, I've noticed lately that it seems to remain up at 8-green for longer (under EV driving) than previously. Normally you'd think this would be a good thing, as it would seem to indicate the battery is holding lots of energy, but it actually seems to be caused by errors in the Prius's SOC estimate. What I've noticed is I can drive (flats) in full electric mode, and it stays up at 8 (then 7) green bars for quite a long time (longer than previously), but when it eventually drops back to 6 (blue) bars, then it almost immediately falls to 2 or 3 bars. It's like it's miscalculating the SOC, and all of a sudden it realizes it's wrong and make a correction of -3 to -4 bars!

Has anyone else noticed these issue?

 

Nah, the battery ECU works perfectly in all cases except for immediately after the battery has been maxed out (like to the point where it's spinning the ICE to dump excess charge). If (for example) it only charges to 7 green bars then the battery ECU monitors the SOC exactly as it should, no unexpected jumps or anything. I'm about 99% certain that this is a battery rather than an ECU issue.

Yeah I'm not 100% sure but I thinks it's 8 year 150000km here. I'd be just in warranty, but I'm certain it wouldn't fail any (dealer service) tests at this point. The car runs great in every other way, gets 55+ MPG and still glides (full electric) perfectly. There's no way this would rate as a warranty issue at this point (in my opinion).

 

Thanks for the info everyone. Yes climateguy, I remember reading you post and was thinking my situation was similar to yours. Especially the part about the wife having to drive it over mountains that take it out to max SOC a couple of times per day.

For those who still think it's just a problem with the battery ECU, let me say that it can run all day, all week, all month, whatever, and as long as the battery doesn't get maxed out then the SOC behaves totally normally. If I'm regenerating then the SOC goes up (slowly and predictably). If I'm running in EV then the SOC goes down (again steady and predictably). If I park it at night with 6 bars then the next morning it's still got 6 bars. If I park it at night with 7 bars then the next day it's still got 7, and so on. Nothing at all seems amiss with how the SOC behaves except for the first discharge cycle immediately after maxing out the SOC (generally to the point of spinning the ICE to dump charge). This seems to be the only instance where the SOC doesn't behave correctly, where it stays up high for ages and then seems to drop very suddenly from 6 down to 3 bars.

 

BTW. Does anyone know of where to look for a s/h battery in Australia, or someone that will ship to Australia?

I do think mine will hang in there for some time (driveablilty so far is not much affected), but in the mean time I wouldn't mind getting hold of a s/h one and rebuilding it.

 

No, if I power off the car and restart then it makes no difference. Maxing out the traction battery charge just seems to put the SOC out of kilter. It stays that way (even if powered down and restarted) until the SOC drops to about 6 bars and then it's like it suddenly figures this out and re-adjusts the SOC back to about 3 bars quite suddenly.

If the SOC was not topped out (like if it only goes to 7 bars, or even if it just hits 8 bars but doesn't top out) then the SOC is tracked properly and no anomaly occurs.

 

This doesn't really sound all that similar to my situation. My battery is hardly ever sitting at odd levels. Actually about 99% of the time it behaves totally normally.

Mine fills up normally but just has reduced capacity (compared to what it used to have). It doesn't just fill up while I'm driving along normally or anything like that. I have to go down a large hill, regenerating all the way, and then it fills up just as it should, first to 7 green bars (normally takes a while) and then to 8 green bars (happens a little more quickly than the 7). This is no different to what it's always done, but over time the size of the hill required to fill it has become less.

Mine doesn't "shut off", but spinning the engine is normal behavior when the SOC is too high.