I bought a set of used battery sticks and just finished reconditioning them and putting them in my 2003 HCH1. The 12v battery has been disconnected for over a day and I also cleared the codes as a sanity check but I am still running into issues. The codes I'm getting immediately are P1555 and P1600. I can't seem to find any information about P1555 at all. After driving for a bit I also got P1575, which seems to often be related to the 100 Amp fuse.

The car will start using the electric assist without any issues. If I disable the battery from the switch in the back, it uses the 12v starter. If I were to guess, the battery isn't being used otherwise, the car seems to coast in gear for longer and not doing regen.

I'm especially curious and interested in figuring out what P1555 is exactly since this seems to not be documented based on the searching I've done.

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I went through a deep discharge and charge cycle for all of the used ("new" to me) batteries at C/10 and tested them under a 10 second 100 amp load, every "new" battery held at around 6 volts and had no problem under load. I tested the old batteries as I was swapping them and 75% of them failed the high current test (most 3-4v under load and significantly more resistance), with some not being able to even source 100 amps.
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I'm pretty confident these reconditioned sticks are good and I installed them correctly. I can read ~160 volts on the main battery terminals. I still had IMA functionality with the old batteries they would just die quickly. Now, IMA is completely disabled.


​​​​​​If anyone has any recommendations on what to test going forward, I'd greatly appreciate it! I'm comfortable with doing any sort of voltage measurements and have an oscilloscope if that would be of use. My only plans are to test the 100 amp fuse tomorrow and determine if it's good or not. Beyond that, I'm pretty stumped as to what's wrong here. I'm pretty sure I connected everything back together.