Yeti 3000X seems dead, screen flashes when "charging" from USB

We bought a van that came with a Yeti 3000X. It worked well for a few weeks and powered an overnight trip. When we came home it sat for a bit under trees so the battery slowly dropped to about 20%. We realized we needed to charge it so ordered the 600W AC charger. By the time that arrived and I plugged it in, it was at 4% but started charging at a good speed. I left it for a few hours and came back in the afternoon to find the unit completely dead and unresponsive.

GZ support said to charge it through USB overnight, but that didn't produce any change. When plugged in this was, the LCD screen will beep, flash, and turn back off every 2 seconds. None of the common button combinations for resetting seems to work since it doesn't seem to stay alive long enough to register them.

We've opened the top like in a Todd Parker video, but none of the wires seem to do anything. I'm not super comfortable physically disconnecting the batteries, but if it's between that and spending $2k on a new one then I guess I can try.

What can I do to to get it back? Support hasn't been too helpful and it's not under warranty since we aren't the original purchasers

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