Dell has recalled XPS 9550 battery for swollen issue.
Bulletin Name: Precision 5510 and XPS 9550 swelling system battery
there are also lots of reports that xps 13 9350 has same problem.
for example,
XPS13 Swollen battery
and
dell xps 13 9350 battery swollen
it's a common issue on xps 9350, dell should recall its battery!