Di2 Failure - Help!

I have a full Shimano Ultegra di2 8070 groupset on my Trek Emonda that until this week was working flawlessly for the past 2 years.
I was on a road ride with a friend and suddenly the di2 died; no shifting, no lights on my junction box, just nothing. I came home and plugged it in to charge thinking my battery was dead; got the flashing red "battery error" light on my charger.
I plugged the junction into my computer and opened e-tube which identified all of the components including the battery.
I disassembled the bike and tried my spare junction B, along with trying all of my replacement di2 wires I have as spares. After changing all of these, the di2 is still completely unresponsive.
My thought it that it's a faulty battery but just wondering what you all think this could be?
I was on a road ride with a friend and suddenly the di2 died; no shifting, no lights on my junction box, just nothing. I came home and plugged it in to charge thinking my battery was dead; got the flashing red "battery error" light on my charger.
I plugged the junction into my computer and opened e-tube which identified all of the components including the battery.
I disassembled the bike and tried my spare junction B, along with trying all of my replacement di2 wires I have as spares. After changing all of these, the di2 is still completely unresponsive.
My thought it that it's a faulty battery but just wondering what you all think this could be?
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Tried to go out on a ride today and shifting completely died, no lights, nothing.
Then when I plug into computer for e-tube, shifting starts working again.
I'm almost positive this is a faulty battery. I figure if it was a faulty wire the e-tube wouldn't detect that component. Any ideas?