HV Battery (Replacement?) Advice Needed

Hi all,

I'm looking for some advice regarding my 2006 Prius with 130k miles. I'm thinking that my HV battery has slowly deteriorated to the point where it's causing drivability issues, and now needs to be replaced, but I have some questions. Sorry for the long post...I'll divide it into sections.

Symptoms

The main symptoms I'm experiencing are rapid charge/discharge according to the MFD and significant loss of power once the battery has discharged to one bar. I realize the latter is "normal," but the problem is that I'm seeing one bar frequently now. Hill climbs that my car used to do with no problem and would drain the SOC to 2-3 bars now cause the battery to drain to 1 bar about half-way up and then loss of speed from 65 mph to 45 mph by the time I reach the top. Descending hills, it's not unusual to see the SOC go from 2 bars to 7-8 bars within 30 seconds or so.

I'm not seeing any error lights, and my (cheap) code reader does not report any logged DTCs.

History

This seems to be a slow degradation of battery performance, rather than an outright failure. I first noticed that the battery would charge/discharge a little quicker than it had been at about 90k miles. At 99k (before the warranty ended) I took it into the dealer and they tested the HV battery. Block voltages ranged from 16.59 to 16.68 V and resistances ranged from 0.025 to 0.026 ohms. Based on this, they said that the battery was fine, and sent me on my way. Since then, the problem has just gotten worse and worse, though.

Questions

My thinking is that I need to get a whole "new" battery - this doesn't seem like an individual bad block (at least based on the readings from 32k miles ago), and I'm not sure I'd be comfortable replacing individual blocks anyway. Do the experts out there concur?

Does swapping out batteries require anything special in terms of tools? Is there any reason the battery ECU needs to be reset or anything like that?

Is it better to get a salvaged battery or a reconditioned/remanufactured battery? I've been looking on eBay and, for example, there's a 2009 battery with 34k miles for $700, whereas remanufactured seem to run $1200-1600.

Are these reasonable prices? Is there anyplace else I should check other than eBay?

Thanks for any help!

 

For those asking about the 12V battery, it's a little under a year old (Optima) and still performing well. 12.84V with no load, 12.10V with load. Also, since this has been an ongoing deterioration over a couple of years and about 40k miles, in which time the 12V battery has been disconnected a few times, I don't think it's a calibration problem (or at least not one that disconnecting the 12V will fix).

As for a drop in MPG, that's a little difficult to answer. It seems like over the past few months, it has dropped a little, but it's also winter. Kind of seems a little lower than past winters, but I wouldn't swear to that. Certainly no marked decrease in MPG.

Well, that's what I've been doing. Unfortunately, that's not really an option any more. The lack of power going uphill means that my wife ends up doing 45 mph on the freeway everyday for her commute, which is both annoying and unsafe.

Another question: I contacted one of the eBay sellers because he has a listing for a battery from a 2009 with 1,800 miles on it. Seemed like awfully low mileage for a 2-3 year old car. He stated that he's swapping cells from a 2011 into the case from an '04-'09. Are there any potential problems with that?

 

Just wanted to provide an update. I ended up buying a salvage battery off eBay from a 2009 with 17k miles ($700 + $150 shipping). Changing out the battery was really not too difficult. Going slow and being very careful, the entire project took me about 4 hours, but it can definitely be done much more quickly. The good news...my Prius is now back to running like it should. It climbs hills like it did when new, and the SOC changes at the relatively slow rate indicative of a battery in good condition.

I think the underlying issue is my wife's commute. Elevation changes between home and her work are such that even when new, the battery would go from 1 bar to 8 bars, back to about 2 bars, and then to about 4-5 bars. This is then reversed on her drive home. So the battery gets fully (within the ~40% limit) charged and discharged about 4 times per work day. Eventually, this just led to decreased capacity to the point where the ICE was frequently all that was left to provide power.

Bottom line - it's possible to have an HV battery "failure" without any error codes. This diminished capacity, though, is probably not something a Prius in the flatlands would experience until after several hundred thousand miles. (Incidentally, I checked the module voltages of the old battery after it had been sitting for a couple of weeks out of the car, and they still all read 7.88 to 7.92 V.)

Many thanks to all the Priuschatters for making this such a great repository of information, which ended up saving me a few thousand dollars from having to take my Prius to the dealer for a new battery. Thanks especially to Seilerts for his tips and helpful posts.

 

For those asking about the battery fan, I thoroughly inspected it and the duct work during the battery swap. Clean, no restrictions, and the fan is operating as it should. Tire pressures are 42/40 psi. The hills are not huge gradients, but are significant and fairly long. I'll see if I can attach a terrain profile.

Again, I think this is just a limitation of current battery technology...the more it gets charged/discharged, the faster it's going to lose capacity. I see this in all my other rechargeable batteries, so why should the Prius be different? (Interestingly, I noticed that the Prius battery modules say "Do not recharge" on them...weird!)

@justlurkin - Interesting idea about using "B" mode. I wonder what the cost/benefit breakdown of that would be. At any rate, though, if this battery lasts me another 130k miles, I might be ready for a new car by then (but I love this one!).

 

@uart - Yeah, I remember seeing that post and thinking, "that sounds like my battery!" At that point, mine was not yet causing serious drivability issues, but clearly our batteries failed in similar manners. Unfortunately for me, no warranty coverage...maybe I should have been more insistent when I took it in to the dealer at 99k miles, but it was pretty clear they weren't going to do anything without it generating DTCs and my only having noticed a slight drop in overall capacity.