SUCCESS!! - Reconditioning Battery - Need some diagnostic help on 2007 Prius Touring

Here is the running numbers on my battery module reconditioning. I am looking for some comments on what looks good, what looks bad, etc. I still have time to do this properly and I really don't want to have to go through this again for a while. It is a quite lengthy process. I'm kinda in the home stretch now.

Some questions:

Many of the modules seem to get somewhere in the mid-5k mAh range after three DCHG/CHG cycles. I seem to b hitting the 7350 mAh cutoff. Should I raise the cutoff to 7500 mAh and try an additional one or two cycles on each module?

I have had a few modules with very low CHG rates after three cycles. Module 25 in particular has had 9+ cycles now and has gone from it's initial discharge of 1604 mAh to 5292 mAh in the last cycle. I have continued to hit them with more cycles and the capacity numbers have been coming up nicely. Am I doing this right?

I did not do load testing of the modules before I started reconditioning my modules. Yes, I know I should have but I didn't. I figured if any other modules were bad, that would show up in the conditioning process. Is there any reason to do that now? Any benefit? I'm still a little fuzzy on just what to do in this test and why. I am still reading, tho.

After I am satisfied that all of the modules have been reconditioned to the best capacity i can get, I then need to apply a load and bring them down to 7.6v, yes? Is that correct? I am then planning to link all the modules in parallel and let them all balance out overnight. Anything I am missing there?

I figure I have a few more days of work left ahead of me. I am anxious to get this battery back in the car but I understand that slow and steady wins the race here. Thanks for all of the advice thus far. It has been very educational.

 

Jeff,

Thanks very much for the response and clarifications. One major question I have at this point: Looking at the data for the modules as I have reconditioned them thus far, would you recommend that I run additional cycles on them at a higher cutoff threshold, say 7500 mAh? Many of the modules look like they are responding quite well to reconditioning. I'm just wondering how much further I can push them to maximize the capacity. And if the answer is yes, would now be the best time to do those load tests, before doing more cycles?

 

Thanks. It has been a bit fun and is quite a good learning process to go through. I think I know more now about batteries than I thought I would ever want to. My main concern is that I don't want to push things TOO far with the modules I have but at the same time, I want to maximize my capacity in this go-around so I am not having to pull the pack again any time soon. I'm probably one of the lucky ones, that I have another car (2006 GTO) to drive while I work on the Prius. I imagine a lot of folks don't have that luxury. Also, all of this battery knowledge will probably get put to some additional use as I look to put solar in my home soon and have battery back up for outages, etc. Not the same batteries, but the knowledge here will be helpful there.

 

This weekend I finished up the reconditioning of my pack. I finished the Dchg/Chg cycles on all of the modules, including the one I planned for replacing the bad one. At that point, since I hadn't done the load testing up front I decided to run through that process now and see how things looked. So I measured the starting unloaded voltage, hooked up the bulb and then measured the loaded voltage after one minute. I then removed the load and let the voltage settle out for another 30 seconds and recorded again. The results are in my spreadsheet linked above. As I expected, every module looked really good except the single, failed module.

I then used the bulb to lower the voltage, under load, to 7.59v on each module. I chose that number because the unloaded voltage would recover to about 7.65v and that was about where each good module was before I started anything. I let things sit overnight, expecting to put the pack back in the car on Sunday.

It was at this point I was about pass up the need to build the custom harness to hook the modules up in parallel. This was Sunday morning and the battery had been sitting overnight so I decided to spot check voltages again. To my surprise, the modules were all showing voltages anywhere from 7.71v to 7.85v. Even after discharging each module exactly the same way, to exactly the same voltage each time, they still ended up settling out with a pretty wide variance of final SOC. I knew I needed to build the harness. So I ran to Lowes, picked up wire and a lot of connectors and built the harness. Once all hooked up I let it sit for 3-4 hours, spot checking occasionally. In the end, every module settled out to exactly 7.80v. So I see the importance of this last step to balance all of the modules.

With a few hours left in the day, I closed up the pack and reinstalled in the car. I left the interior pieces out, in case this went bad and I had to pull the pack again. I started the car and voila! I had a READY light and no warnings! The engine ran very rough for 15-30 seconds, presumably as the computer started to adjust the timing given the car was completely unpowered for over a month. I let the engine run until it shut off. The battery appeared to be charging and power bars were in the blue range. I took the car for a quick trip around the neighborhood, which is a few miles and some good hills. All was well, no codes, and even got well up a significant hill completely on battery at 15mph before the ICE kicked in. I was impressed. I drove the car to work this morning (about 10+ miles) and everything ran great. I'll hold off final judgement on the complete success, but things look good right now.

Things to still do:

I need to reassemble the interior. Will probably do that later today after work and a successful trip home
Need to check things with techstream, though my "evaluation" copy/license seems to have expired. Probably need to do a re-install.

So thanks to everyone who responded to my questions. This is a very knowledgeable community and hopefully my experience here will be of help to others. With any luck, I'll get another 123,000 miles out of my pack.

 

I did check the fan and it didn't look all that bad, considering it had 9 years of service. I didn't pull it to clean it, and knowing now how easy it is to get to, it's not a problem to check it a little more frequently. Also, now that I have a mini-vci and techstream, I can do a bit more frequent checks on the pack, temps, etc.

I am happy to report that I've got the whole car back together. I can carry passengers again, YAY! The interior went back in a lot easier than I remember it coming out. I have about 150 miles on the car since the battery went back in and things have been working great. I'm seeing good increase in MPG now vs before the build. I have been averaging 48-50 MPG so far. We'll see how long that lasts.

 

Just thought I would post a quick follow-up. My Prius has almost 5000 miles on it since the rebuild of the pack and not so much as a hiccup. It's been running great.