I’m on holidays, tomorrow is my last day and my r8100 di2 suddenly stopped.
Even when plugging in my charge cable I see no leds. I plugged and unplugged both my rear derailleur and both cables into the battery in my seat post
Not helping I know… but the quickest solution is new bike day. Go mechanical! 
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Found this
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Disconnect everything except the battery and the junction box with the charge port, and see if it charges.
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The battery is almost always connected to an intermediate junction box near the bottom bracket. Check the connectors here.
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If this doesn’t fix it you’ll need to do some stripping down and connect the battery directly to the charger via the charge port and see if it’ll connect to a PC. A bike shop with the proper diagnostic tool is helpful here because they can connect components to it using e-wires.
Really if that doesn’t help you’ll need a local bike shop willing to test a known good battery on it, or take a chance and order a new battery yourself and return it if it isn’t the problem.
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Had the same issue, di2 was completely dead (no blinking and no charging) - solved by updating the left shifter, front derailleur and battery pack (used software v 4.0.4)
Had this issue with it being a cable had become damaged with water. No option but to single speed the last day of my trip. Plus you get to learn if you enjoy single speed.
It was definitely a faulty cable but I didn’t feel like riding up the Cime de la Bonette (again to try and finally get under 100 minutes) with 52-34 as my easiest gear…..