I have a new black 107 that I received on Wed.
I charged it yesterday for five hours and I got 8-12 minute sessions on,so a total of 96 minutes of use.
The charge light came on when I tried for a 9th session
I had temp set to 6 and bumped to 7 at the last 2-3 minutes before shutdown on all sessions
I got about 1-1/2 stems per 12 minute session. Small dome screen in stock stem.
So an hour and a half on one charge isn't bad,hopefully batt time will get better with usage.
Edit to add I usually shut solo off after a stem,I ran the above letting it run a full 12 minute session.
And I gave kudos to ataxian for the batty fix.
Can I ask where you got your solo M-107