Prius High Voltage Battery Reconditioning

(Question: How would you prefer us to add or change stuff on this wiki? Should we keep our comments separate in parenthesis like this? Or do you want to do it differently than that? -OP:I don't know, maybe don't delete anything, but add your thoughts...)

It's time for a HV Battery Reconditioning Wiki Page. For now, it's based on my experience of 30 days work on the Gen II Prius. Please feel free to add your knowledge, changes, corrections, enhancements. More documentation is needed on how to simply measure internal resistance and to correctly pair modules into blocks before reinsertion in the mended HV complete battery.

See also: (PC summary of earlier work by various PC members) Prius Traction battery repair summery | PriusChat

Youtube: (some of the better videos)

("Ultimate Guide"):


(best method for holding modules/getting modules back into the HV case):


I completed my rebalance/recondition/cleaning of the Gen II HV battery and fan. It took me about a month, because of having to relearn soldering, acquire the correct hobby chargers and banana/alligator/wires, replacement modules. I could do it carefully, slowly again in 2 weeks, given the slow and steady DSC limitations of the multiport charger I bought.

While it's fresh in my memory, here are some things that I (30 days ago a neophyte, now an intermediate HV battery person) would note should be in a wiki or for anyone doing this for the first time:

These are my notes and not a complete HOW TO, not covering all the steps and safety concerns. Working on a car or electricity is inherently risky and you must know what to do, or at least what not to do. I suggest people review these against what they've learned elsewhere and only proceed after lots of prep with priuschat, youtube and other sources of research and knowledge.

This is a complicated but not difficult process that requires effort, planning, time and thoughtfulness. An unhurried persona can do this, particularly if you're not completely confused with batteries and basic electricity. You undertake work on your car and HV battery at your own risk. Learn more than you need to know, go slowly, test everything for voltages. These are notes to complement what you learn above in the links and on the web.

PREP / First Steps
Read the Priuschat HV battery reconditioning /balancing summary (above) and peruse the long individual chat threads.

Watch several shorter and several long Youtube videos on Prius battery repair, including the "Ultimate Guide" and the ElectronAutomotive removal/replacement videos (above).

Decide if you will do the whole thing, or just order and install a rebuilt HV battery. If you need your car to be back in service in less than 2 weeks, maybe you should just buy the reconditioned battery and install it. On the other hand, it's a great process to do the whole thing yourself - I'm glad I did.

PREP / Check the car's OBDII data
Find a way to check your car's battery status via the OBDII. There are different apps. I used a Bluetooth generic OBDII reader with an android phone or tablet and the paid but inexpensive Torque Pro app. I downloaded and installed the free "Prius PIDs" to Torque. That was complicated and took me a day to figure out! That will tell you what your battery's 14 banks are registering and the difference in charge between them. It will be clear which of your blocks are weak, if any aren't close to the others' voltages. You might jot down the values (Blocks and Modules are counted from the non ECU/computer side on Gen II cars and the other way on Gen I cars.)

PREP / Decide how much you'll do - Buy your supplies
If you do the whole thing, invest in the hobby chargers needed to charge 4 or more modules at once and buy/make the AC/DC 12v power supply to power the hobby chargers. Watch out for the imax and detrum fake/copy chargers. It would be much better to spend more and get a great multiport charger that can discharge quickly and can run 3 or more dsch - chg cycles...than to buy cheap iffy chargers. Source a torque wrench and figure out how it works. Ditto for a soldering iron/gun, in case you have to make your own banana clip/alligator clip leads. You can do it!

Learn how these complicated hobby chargers work - there is a crazy menu structure with some of the important settings under "User Settings" and some under NIMH Charge[x] If you can calibrate your charger, do it, otherwise know how much off it is vs your multimeter and plan accordingly.

Figure out what safe but useful reconditioning settings you will use: I used CHG @ 2.5A inputting 7250mA, no time limit, DSC to 6.0v with whatever Max DSC Amp rate you can get. I chose 3 cycles, but stopped earlier if the DSC value (the one that matters) was high enough (above 5K or the same as my other modules) I used a Turnigy 4x6s because it was the one I found online available new with an Xbox 360 power supply I carefully converted (soldering a T60 hobby connector for the 4x6s charger) to make a 12v PSU. This is geeky, I know.

DISASSEMBLY - Interior
Disassembly of the interior and the bolts holding the battery down isn't hard, but you definitely want to use some system (ziploc bags with masking tape and marker explaining to you what everything is) to store the hardware you take off. There is a lot of it and it's hard to remember where it all goes later when you put it back. The interior will all fit in the front and back seats. You can put the hardware bags or containers on the dashboard. Pull the Orange Safety plug from the HV battery before you move or open the battery. Don't lose it or forget it later!

REMOVE HV BATTERY
Note you already removed the orange safety plug above. Move the battery from the car to a place it can sit for the week(s) while you work on it. Two people with gloves (sharp edges) is best. It seems to weigh about 50-60lbs. I did it myself. I put a board (1"x4" x a couple feet) I had lying around down between the bumper and the battery. Using this I could slide the battery slowly up and out (and later in and down) without hurting myself or the battery or the bumper.) I put it on some thick towels on a table in the basement, close to a powerstrip. Read all the safety information and wear gloves especially until you understand.

RECONDITION HV BATTERY
Recording in a spreadsheet or notebook, write down what you've done and what you're going to do as the project progresses. This process has lots of steps including: purchasing replacement modules for those determined to be 'bad' (below 7v), performing multiple DSC/CHG cycles and recording the improvement/final DSC value, Finally charging all the modules to within .05V of each other, Lastly connecting the + terminals (only) and the - terminals (only) so the 28 modules are all in parallel and balance

EDIT 1/2021: PriusCamper mentions putting balloons over the vent holes (on the top) of the modules while you charge them to both contain Hydrogen Sulfide gas - and to get a sense of how much heat/stress the module is under. I wish I'd done this and recommend you do it too. - you don't want excess Hydrogen Sulfide entering enclosed spaces where you work/live.

I purchased an inexpensive ($25) Wyze wifi security camera that could send live and recorded video to my phone - and would alert me when my chargers went 'beep'. This was incredibly helpful and I suggest you consider some sort of video camera/alert thing, unless you plan to sleep and live by your battery while your chargers do their work.

Note that you should only charge modules when they are in their 'rails and white blocks' fully compressed. The compression rails and blocks can be removed from the HV battery shell, and I suggest you should do that.

Module Replacement
Replace modules that fail to grow their DSC values to be similar to your good modules. In practice none of my 4 'low voltage' modules every got better. I bought 6 modules and used 4 of them. I felt my other modules were OK.

Module Matching
Module matching seems like the murkiest/most mysterious part of all this. It's suggested to do multiple things all in synch: 1. Given that middle modules are exposed to the least venting and most heating, move these to the ends (and vice versa). 2. match modules with similar internal resistance together, 3. match pairs of two modules so that their overall total capacities are all the same. I'm not sure I did this all correctly, but I did 1 and 3...I hope.

Final fiddly adjustments: Charge/Discharge each module so that it is within .05v of all the others.

Last balance. Attach all modules' + terminals and (separately!) all - terminals, creating a very large parallel battery. I flipped every other of my modules so all the + terminals were on one side and then connected all the positives with a long thickish solder strand - flexible, conductive, easy to work with - and bolted down VERY LIGHTLY. Connect all the negatives likewise. Let sit 24 hours to balance. Then carefully disconnect, saving all your nuts. Carry out your final ordering of the modules in their rails/blocks. Tighten the rails appropriately then The modules/rail/block assembly can be put carefully back into the HV shell.

REASSEMBLY - Battery
If you did it the easy way, you already have all the modules in their rails/blocks assembly and it's separated from the HV battery case. Verify that your positive and negative terminals alternate and start in the correct position at module 1 and end in the correct position at module 28 - this is very important! Connect the 3 or so heat sensors. Originally they were on module 1, 28 and 7 on my battery. On advice I moved them all as close to the middle of the pack as I could get, since that is the part that builds heat. Carefully turn the HV battery shell and rails/block/module pack upside down. Screw in the 28 alternating bolts torquing just to 48 INCH pounds. (In fact don't trust me or any other poster on torque values EVER without triple checking...) If the holes don't line up with the modules properly, you might have to loosen or tighten the 4 bolts on the rails/white blocks a bit.

Busbars - coating / torque
Working on one side only, replace your cleaned up busbars and nuts. If you didn't already do it, you definitely want to clean the copper busbars. I put mine and the copperish nuts in a cup of white vinegar for a few hours which cleans the (basic) corrosion. Then I washed them, scrubbed them with steel wool or a Scotchbrite kitchen scrubby and washed again with baking (neutralizes) soda and water. I dried them all and then kept in a safe place - don't lose!. Before reassembly of the busbars coat them in a conductive anti corrosion coating like Noalox. Carefully use only a torque wrench to tighten the nuts back - I used 48 INCH pounds. Practice on your bad modules if you're not sure what it will feel like when the torque wrench clicks. Apply the black safety covers over the orange plastic/copper busbar assemblies. Do the other side.

Close up the battery carefully (do not connect orange safety plug - that's your last step before turning your car on again!

Return battery to car, bolting everything down.

HV Battery Fan
If you didn't already do it, you definitely want to remove the white 12v fan and remove its cover and duct work for cleaning. Reportedly, HV batteries fail because of filth build up in the fan and ductwork. You've spent countless hours on this project - this is easy and you can do it: remove all the dust and build up from the fan blower (easy to remove the cover for good access). Under the sticker on the Toyota motor for the fan is likely a little metal shaft. Put 2 or 3 light motor/bearing oil drop in there and let gravity pull it down to lubricate the fan.

Working by yourself slowly, or with the help of the Youtube videos /notes you took on where everything goes and with which fasteners, put it all back together. You may want to pause after the battery is safely attached and covered (and the 12v battery is attached again) to insert the orange safety plug to test whether all your work is GOOD. Recall the orange plug has three motions: Push in, flip up, pull down... If your car starts and the errors go away, great! If you get an error, consider checking your work. If no obvious mistakes made, try the car a second time - some have said errors clear themselves on a second restart. If all good, continue putting the car back together.

Even if something isn't quite right with your modules, you can check them with your OBDII/Torque etc solution and find out what modules are the issue. You already know how to do so much, you can carefully consider what went wrong, and resolve it, perhaps with better module balancing, module pairing, module replacement or more DSC/CHG conditioning!
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Here's a little picture you want to avoid... (lesson: work carefully, make sure you trust your hobby charger, don't attempt to 'monitor' your charging process yourself without charger control...)


I write this for you and also for myself, in case I have to come back to do this in some years (hopefully many) Good luck!