It's not a low battery. The front derailleur keeps working as usual until the battery charge is down near zero -- the indicator light is flashing red.
Then it turns off the front derailleur, to allow the rear to keep shifting a little longer (supposedly about 50 rear shifts?)

That looks like an 8050 front derailleur. I replaced my 6850 front when one of the the metal linkage bars snapped, after 8 years and 33000+ miles. It still made a normal shifting noise, but just didn't move the cage, of course.
The 8050 has a sturdier, redesigned linkage and was a plug-and-play replacement. (But I did have some annoyances getting it aligned correctly -- that's tricky)