There are a couple things that I would try if it were mine. 1st I'd copy the .ecig file using EScribe. Using Escribe do a hard reboot. Still not good restore to factory defaults. Use Evolv's default theme. EScribe creates a backup so either with that or your saved ecig file you can always return it ti as before your changes were made.
If you have previously connected it to your computer EScribe has created a backup.
Start EScribe , go to Tools/ Backup. Search by mod/board and date, apply, update to mod.
As far as firmware. you should use the latest.
I wasn't expecting to see a a post about a Darwin, ever. I suggest that you open a ticket with Evolv. Your cable and and any USB power source should do, must be more to the problem.
https://helpdesk.evolvapor.com/index.php?a=add&category=1
My DX200 (not DR200) was the earlier version. I still have the case and had a look at it just now. That plastic piece should have a sticker on it covering the screws that hold it in place. There are 3 on mine the same location and pattern as the board mounting holes. The three screws screw into three standoff screws which hold the board into the case.
I have or had quite a few DNA mods powered with a FullyMax 900 mah battery. Keep in mind that it has the same capacity as a 30 amp 2700 mah 18650. I have my doubts as to try to fit in a larger battery.
What wattage are you using it at ?
Have a look at this thread:
https://forum.evolvapor.com/topic/72119-dna-100c-wattage-drop-after-3-puffs-geekvape-z100c-p-coils/#comment-940230