I have done exactly the same thing after Giant said nope can’t help. And two cells had also leaked (one of the corners) bizarre. Looked at the price of new batteries might just scrap the bike.
Hi did you ever get to the bottom of this? I have exactly the same error code, possible addition maybe that on the charger side its continuously flashing red, which suggests the charger isn't communicating with the battery?
Im waiting on a reply from Giant, but wondering whether you managed to...