Help with diagnosing my battery issue?

First, you probably should get a new 12 V battery and connect it to a tender when not in use.
There is a small but very real chance that will keep it happy for a while longer.
Repeatedly running IT down undoubtedly has done it some harm.

Then, when the time does come that the HV battery needs work.......unless you like playing "whack-a-mole" and taking it apart every few months to change yet another module......you should consider getting a whole battery rebuild or a new one.

How much longer do you think you might keep this ~20 year old car with ~200,000 miles on it running ?

 

The point is you'll be taking this battery apart many times doing the dance replacing a cell at a time cleaning up bus bars and nuts etc etc You might want to get somebody who rebuilds battery to whip you up a rebuilt battery with new or clean bus bars and new nuts and all that sort of thing so you're not playing whack-a-mole essentially this is a very real thing If you have lots of time and your time is not worth much to you than by all means proceed but I paid the hybrid doctor guy up in Virginia I think $650 for a complete rack built balanced looked brand new nice looking setup and it's been running great ever since I don't know what it's been now 7 8 9 months. And no issues That's how I like it If I would have started replacing cell at a time and that kind of business I would have just left the whole battery in the back exposed because I know I'm going to be taking it apart and reassembling it quite a few times you'll get good at it but it's not really a lot of fun and you don't get to see the fruits of your labor very well because in the end you'll probably wind up with a rebuilt battery that's just easier when you have all the equipment the big chargers and all that sort of thing It goes faster and flows better that's why they can get that done reasonably I'm not 650 is nothing to pay that to me that doesn't bother me a bit now 16 to 2400 that's another story but I did that in my generation too like yours and again haven't looked back I see the green a lot The car runs great and I'm at 300,000 so I got 100,000 more than you and I'm looking for 600 and I should get it I have no intent to sell or get rid of the car unless somebody rams the hell out of me and tears it up then I'll transfer all those parts to another Gen 2 You can get these cars for near nothing now and all kinds of conditions

 

Read my post again.
Even "new" batteries sometimes go bad.
Especially if they are run flat more than once.

 

If the 12V goes "dead" several times, that can damage it to the point where it no longer can hold a charge.

The HV battery ecu monitors the voltage of 14 blocks. Each block is two sealed modules. So there are 28 modules total. One of the two in block 4 is bad. Possibly others. On a Gen2, module 1 is furthest away from the ecu, so your bad module is #7 or 8- those two make up block 4.

I would hit the "record" button on Dr Prius & go for a drive. See if other blocks are consistently lower than others (by more than 0.3-0.5V) on discharge or higher on charge. On that first pic, I am suspicious if block 8 & 11.

"Just" replacing modules can work, but has a very low chance of success. More often, the replacement has different (actual) capacity or state of charge. It now has higher voltage level than the others in the pack - the "voltage difference" is too great and the ecu codes the next lowest block as "too weak". It might only be apparent when the pack is stressed by actual driving. So you replace that module. It happens again to "the next lowest". Repeat in a game we call- whack a mole.

If you go into it yourself, read the service manual cautions for safety. Find some youtube videos. Take your time. Rushing will end up breaking things. You need an INCH pound torque wrench to secure the module studs. Inspect the battery sense harness for damage and corrosion - esp at the ecu connector.

Good luck, you WILL need it.

Posted via the PriusChat mobile app.

 

IMO, No 12v battery problem is going to cause false module voltage readings. Especially when the car is in READY.

You can easily do a load test on the HV battery using your AC system. Get the car completely warmed up, so when you park the engine will turn off and stay off. Use whatever app you used for the first photo and turn the AC on max. This will draw anywhere from 6-14 amps from the HV battery depending on outside temperature. Watch your block voltages. Since the car shouldn't start until the HV battery reaches ~42% SOC, that graph should be relatively steady and each block voltage should slowly drop. A low capacity module will cause its block voltage to drop much faster than the others as time passes. You should be able to watch those graphs to see which modules are a problem. It's likely more than one. As soon as the HV battery reaches ~42% SOC, or if a module drops very rapidly (which will trigger the 42%) the engine will start and begin charging the HV battery again. Sometimes a module will drop so fast near the end of the test that it will trigger the P0A80 code before the engine even starts.

 

You need a 12 volt that maintains 12 volts overnight couple weeks what have you doesn't matter what kind the battery You just need it you know a good 12 volt battery that's capable of running all the lights and all the computers and everything on the car it's not really that big of a system . Seems to me this car would be like a perfect candidate for a lifepo battery like some of my powersports equipment has lightweight blah blah blah and not having to roll a starter around this car should be a perfect candidate for that.

 

All you need to do is remove the trim piece expose your battery get the case top off and have a look at your bus bars nuts the front end where the board is and the little plug I think it's brown or orange that goes to the control we need to check all those for burnt pins anything that doesn't look right etc all of this stuff is available The cars are plentiful in most places You may have to call around

 

What about this:

I think you will be making a serious mistake tearing into the HV battery before making sure that your 12 V system is healthy.

 

If that really is a cheap, unregulated "trickle charger", you should throw it away and get a tender type battery maintainer.

Given your situation, your HV battery likely needs some attention.......or will soon.
But your 12 V likely didn't get that bad all of a sudden and may have contributed to HV faults showing up sooner than they should have.

You need to "fix" the 12 V battery FIRST.
And that does not mean charging it every day.

 

And after that, it is likely YOU who will be playing whack-a-module every few months.