This is such a coincidence. I've got a 2021 Turbo Levo, was working fine just a few days ago. Took it to my LBS today for the bike's first service since purchase - they tried to turn it on, and it was dead. No lights on the TCU. They initlaly thought the battery was completely flat, but last I looked (a few days ago) it was 80%. They plug in the charger, and only the 3rd green LED from the bottom up was flashing.
While they were trying to work out what the problem was, Google found this very thread, and also this post from 2019
I plugged my battery into my 2019 Levo this morning and it didn't turn on. Took battery back to house and placed on charge. One single green light flashes. Anyone know what this indicates. I charged it up fully around a week ago and have not used it since, it's been stored on my house, not in...
www.emtbforums.com
The exact same issue.
LBS calls Specialized support, and I heard something about "battery low voltage" and the fix is to replace the battery. Luckily my LBS had a brand new battery in stock and they just swapped it.
So after only a few weeks of ownership, I'm on my 2nd battery. Mass kudos to my LBS who just swapped the battery without a single hesitation. I'd still love to know what the actual reason is for the 3rd blinking LED - if the battery has dropped a cell, water ingress or whatever.