Yes without a battery the Switch won’t power on.
Not sure if it will still work with a dead battery though, but it might get so swollen that it will have to be removed regardless. The back of the Switch looks like pretty thin plastic, presumably to allow the battery to expand. I wonder if that plastic will crack or the PCB’s could become damaged from the pressure over time?
Regardless very few will ever replace the battery, most will probably just recycle a non working console, and even fewer will mod it like this to keep it working docked.
I rarely use my Switch anymore, but last night we wanted to play Snipperclips. With no charge in the battery it took at least 10 min before I could turn on the console in docked mode. Another annoyance to look forward to for retro enthusiasts. It won’t be plug and play like other systems, so that’s actually another good reason one might consider doing this mod. Because that should allow for instant booting
