According to your update it seems the screen has no more issues, right ? What you’re doing to start up the Mac is a SMC bypass, it works to see if Mac can boot but shouldn’t be used, unless for shorter times, as SMC is essential to run things correctly..try an SMC reset instead.
If that doesn’t help unplug the battery from the board and see if things get back to normal. Unless you already glued the new battery in place it would be useful to reinstall the old battery to narrow down possible causes of your issue.
It might be a faulty battery or a faulty SMC circuitry at this stage and without further info.