Dead HV Battery on 2007, hoping for confirmation.

Hello everyone! I've been working through similar posts on the forums and elsewhere and think I'm clear on what's going on, but hoping to get some more expert opinions on if I'm right.

I have a 2007 Prius, with no major issues prior to now (e.g. just things like the 12V, HID headlights and ballasts, etc). Unfortunately and foolishly, I decided to mess that up by letting the car sit for about 6 months without being regularly run. It was running without any trouble prior to that, and while I knew there may be some trouble after it was sitting for so long, I had expected the brunt of it to be on the Aux battery. As expected, the 12V (an Optima Yellowtop) was definitely dead, but after careful jumpstart attempts I still couldn't get the car into Ready mode. I took out the 12V and used a charger, and as expected it wouldn't maintain voltage overnight (dropping from a full charge to below 11V by the next day). I got a new Yellowtop 12V and put it in today, and still cannot reach Ready mode, furthering my fears of it being the HV battery. I know that the HV wouldn't have any direct drain on it while sitting, but wasn't sure of the state of charge when I last used the car, so uncertain if just standard NiMH chemical drain would have been enough.

As of currently, the car can enter all states except Ready mode. When trying to enter Ready mode, I hear a relay clicking in the back of the car (around the area of the HV battery -- sounds like it's on the 12V side of the HV), and the Ready light flashes a few times, but then I get the Red Triangle and a Problem alert on the display. Also, seeing other issues I've already verified that the Brake Light is working fine, so doesn't seem to be any issue with the brake components not engaging and preventing Ready mode. Planning to check more into this once I got the new 12V, I got a Bluetooth ODB scanner and Torque Pro, and checked a few things today. First off, the only error/fault being received is P0AFA, which I saw online is an HV Low Voltage. I also had installed the Custom PIDs and checked on the HV Blocks and HV SOC. Assuming I set it up right, it showed HV SOC at 43.0 -- and Blocks 3 through 14 are sitting at 14.8/14.9 Volts. Though these are low, my bigger concern was seeing Blocks 1 and 2 basically dead (Block 1 at 0.9, and Block 2 showed as -0.6). The one concern I have with this is that this is being measured from an attempted start, but without Ready mode engaging. I know in this situation the SOC listed on the display is a guesstimate, so I wasn't sure if the data fed to the ODB would be accurate for HV values if the starting relay never engages and Ready mode isn't entered.

My thoughts from the above is that I had a dying HV battery (I suppose not surprising in a 2007 that's been very heavily used), and it drained down too low while sitting. I had hoped a dealer with a grid charger might be enough, but I'm afraid that just topping up the charge on the HV wouldn't be enough given what's showing for Block 1 and 2. Given all that I've seen, I was thinking it's pretty safe to say that I'll need a replacement HV battery. I'm hoping I can get some confirmation, or other ways to interpret what's being seen, before I proceed. I can handle some basic stuff (dealt with the 12V, HID ballasts, etc), but any HV work is something I wouldn't dare to tackle on my own. Going to start pricing new OEM replacements at a couple local dealers, as well as check on some potential independent Hybrid groups that will come and pop in a remanufactured HV (depending on price may lean towards this, given the age and value of the car already). But hoping to go into this with as much certainty as possible (without directly dealing with the HV unit) to be safe.

 

Thank you both for the responses! Sorry for the late reply, posting right around the holidays was not the best timing on my part. The car has just short of 172K miles. I definitely understand the discrepancy with the SOC and the voltages I mentioned, but I may be using the incorrect metrics within Torque Pro. For that reason, I'm attaching a few screenshots, not just of the meters I had set up with the block voltages, but also some other screenshots of live values where I saw something that I figured may be applicable to the HV battery.

Trying to get the pack charged first makes perfect sense, though I know it may or may not be successful, since some blocks may be truly dead/shorted. I think my primary concern now is the "how". I doubt I'd have the best of luck through a dealership, as I'd imagine a full HV replacement is the go-to solution there. That said, though I'm in Virginia, I'm not in a metropolitan area (about 1.5 hours out from DC), so my other options are a bit more limited. I did find a few independent hybrid repair/replacement companies based in Virginia that may travel out to where I am. That said, I wasn't sure if a recharge is something that would be on a "we come to you" type agency, as I wasn't sure if the recharge would be quick, or an overnight process. I'm definitely up for trying a charge and/or balance first, but not sure about anything extreme like purchasing and using my own grid charger when it's quite possible that the blocks may truly be dead, and a replacement may be needed.

Thanks again for the insights and the help on this! Thankfully the repair isn't an immediate issue, so I have some time, but am hopeful that I can get the Prius up and working again!