single cell replacement in HV battery

I replaced a single module in my 05 HV battery. Bought a cell off ebay and installed it. Being in a hurry and not knowing any better did not balance the module. Have put a little over 2000 miles since replacement. Car had 157k miles on it and mpg averaged around 48 since it was new. After the cell replacement mpg is around 57.

I'd be interested in others experiences with single cell replacements. Did it work, did it last etc. Did your mpg change? Whatever.

thanks
update
For those who may be thinking of replacing a module without balancing I suggest that you view the thread Gen II Prius Individual Battery Module Replacement. After researching the issue I have concluded that it is not a good idea. My results were apparently good but that may be the exception. I have ordered a used O9 replacement HV battery. When it arrives will swap it with my 05 pack, properly rebalance it and keep for a spare for the 3 high mileage gen 2s in the family.

 

Hey Steve, thanks for the reply. No monitoring of battery. Yeah I don't get it either. I am no hypermiler but drive pretty easy. About half of miles are interstate and the rest rural two lane. Not a lot of city driving. Have filled car four times since replacement. Tanks have all been between 56 and 58 according to both pump and monitor. I am surprised at how close they agree. I really never paid much attention to the monitor before but since the change in mpg immediately caught my attention I have since. Running about 465 miles per tank. Fill ups are pretty consistently around 8 gallons. Prior to change I rarely got over 400 miles out of a tank. Another piece of info is this, I bought another 05 a week ago for my daughter. It has 145K so I changed the cvt fluid' did routine maintenance and drove it for about 200 miles to make sure it OK before turning it over. I was getting about 56 out of it according to the monitor. I might be sort of a natural hyper miler. But anyway I am sort of wondering if the module that failed was weak from day 1 and if it was not limiting my mileage all along.

 

I generally run about 65 on the interstate as long as traffic is light which it generally is. In heavy traffic I pretty much go with the flow.

 

you make a good point, it is definitely my low speed and city that has improved the most. Best I ever got in the past was 55 mpg on a long interstate trip. My low speed was what was dragging it down. Now it goes up in low speed. After I leave interstate average steadily goes up. Yes plenty of hills and small mountains. Both times my hybrid alarm can in was in city driving. It actually cleared up on the interstate. That was before it went into safe/turtle mode which occurred in city driving.

 

Yes we have ethanol blended to as much as 15% according to the label on the pumps. Maybe it is 10 instead of 15 don't remember for sure. Tires are Goodyear Viva Authority. Had them for several years so don't remember for sure but recall that they are low rolling resistance tires. I am not religious about checking them but try to keep them around 35psi.

I think my mpg is mostly due to gentle driving and also I run the AC only when it gets around 90. I do most driving either early or late when it is not so hot. I work outside and am fairly heat tolerant. For high speed I use diagonal cross window ventilation. Open right rear a couple of inches and drivers window maybe 4 or 5. Read somewhere that doing so minimized the aerodynamic impact of opening windows. On low speed back roads I just open them on up. If I do run AC set it for 80 and I am fine with high speed fan. I have never checked mileage while running AC continuously so don't know what the impact be. Probably depends on outside temp and inside setting.

One thing that I do know for sure is that having a bicycle on the back rack at interstate speeds knocks mileage down somewhere in the range of 20 to 25%. Maybe even worse It is so bad that it makes the engine strain. I generally haul bike in the back instead of on the rack if I am traveling more than 50 miles or so. I can get two in there OK. The bike I am reckoning disrupts the air flow over the back of the car and creates a lot of drag.

I can't think of anything else that I do special that most other prius drivers don't do. Run a standard air filter, standard plugs. Use synthetic oil. No modifications. Wash the car every other year or so.

If I think of anything else will pass it on. BTW I did not realize that there was anything special about my mpg other than the significant change.

 

One other thing that I try to do is to leave the windows cracked if the car is out in the sun. Better yet keep it shaded if you can. This reduces AC load in the first several miles of driving and maybe more importantly provides cooler air to the battery. Checked my closed up truck vs my prius with cracked windows. Using an infrared temp sensor, truck interior was at 123 seat level prius was at 92. It takes a good many miles to get the heat out of the interior.

Went into my battery pack today and checked cell voltages to see how things are going. While I was there cleaned out the battery blower. It was pretty bad. Might be a contributor to the failure. Pretty simple. Take the boot trey out, the right upholstery side panel and maybe the piece velcroed to the seats. Be able to see it all from there. Separated halfs of blower housing to clean, used a small paint brush and kitchen sink. Less than an hour job.

Back to the battery. Cell voltages ranged from 7.73 to 7.78. the one I replaced was at 7.77 so it seems to have settled in OK. Replaced it 2300 miles ago. From what I have found online that seems to be typical but I am not ready to declare victory . Reason I checked it today was that I am leaving on a long trip next week. I am taking a charged up spare cell with me and the tools to replace another should I have an additional failure. Not a job that you can get done at the local garage.

 

Update on Prius along with some new weirdness. Instrument cluster and Poor low altitude MPG.

Car had 157+K when the HV battery failed. Now has 165+K. Just completed a 6500 mile trip over 20 days. From the southeast to Oregon, down through California high country and back via AZ, NM, and Texas. No HV battery problems but did have others. Fortunately minor. On way out in Glenwood Springs CO on about 40F morning instrument cluster failed to boot up. Energy monitor was sort of working but not displaying mileage data as it had lost input from cluster. Car would not shut off normally but ran normally. Long story short. Dealer was handy. Diagnosed as instrument cluster failure. Toyota has a service bulletin out on issue. Way to shut off car is to hold power button down until it shuts off. Cluster is a special warranty item to the end of this month. Takes four days to get and install. Could not wait four days as had to be in Oregon in two. Got it to shut off and when restarted cluster came back on. Behaved normally until about 10 days later on another cool morning had repeat of issue. Same story. Told service guy that I had installed optima battery and he said that they are temp sensitive. Two years old. As a precaution, bought another battery from dealer and took it with me. Have not installed – yet. Forgot how to get into battery diagnostic mode so did not check it on cold morning. Will do when I get a cold one here which may be a while. If battery is weak will install new one, otherwise will go in daughter's car which I suspect has original battery.

On to other weirdness. Spent several days and many miles at high altitude. Car did fine. As soon as I dropped down to low altitude in west TX mileage went from 50ish to 42. Was running mostly at 75 which is speed limit on major TX back roads. Change was apparent when I dropped off a 1000 foot escarpment. Stayed that way until got home 1200 miles later. Slowing down to 65 did not help much at all. Maybe 1 or 2 mpg improvement Monitor and gas pump in agreement. Mileage sucked. No changes in speed etc. Upon arriving home did my informal capacity check on HV battery which consists of running in EV mode for .8 miles with a 40 ft elevation gain. Looked normal. Lost 4 bars.

I am guessing that the car computer had adjusted gas air mixture for high altitude and did not reset upon returning to low. Disconnected 12v battery negative terminal and let it reset to default. Short test drive. Let car warm for 5 miles and reset monitor. Drove 7 on interstate at 65mph and 4 on city roads. Monitor says 67 averages. Seems to have worked.

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I'd have suspected a bad tank as well, however mpg drop occurred in the middle of a tank. Was immediately obvious and did not relent with 3 fill ups. After resetting CPU car is back to its old 50+ mpg now. I would have reset it on the road but that would have involved unloading a ton of junk to get to the battery and running the risk of creating some other problem while away from home. I suspect that there is an issue with the car as I would think that it would adjust to the lower altitude on its own. Granted I had done a lot of high altitude driving, some upwards of 10K feet. It could be that the car is like its owner- a slow learner.

I posted this question stand alone as another thread, one guy suggested that my issue was high speed combined with higher density air. High speed certainly was a factor but there was definitely something wrong. Avg mpg was at least in the high 40s at beginning of trip at the same speeds and at low altitude with generally unfavorable winds . Some very unfavorable.

thanks