I pulled the battery and pressed the Reset button whilst reconnecting to USB. This got the device to boot and be detected correctly. I couldn't erase the bad flash, but I flashed the stock firmware back using M5 Burner , this worked.

I had a similar issue after a bad flash. I had to pull the battery to get it to boot and enable a clean flash. After re-connecting the battery it would not boot on battery only. I assumed the battery was dead. I plugged it in to charge for 5 mins, then unplugged, then replugged for 5 mins, I did this 2 or 3 times, then left it to charge for 30mins. It's now fully alive. My understanding is sometimes the batteries get slightly over discharged and won't charge, plugging in and out gives it a little boost to wake it and start charging. This is from my experience with other battery devices.

i couldn't get it to install on my device. How did you do it ?