It is technically possible to replace the Samsung Galaxy S6's battery - Phandroid
iFixit teardown reveals Galaxy S6 battery replacement is a really tricky job
for Samsung Orginal Battery 3.85V 4000mAh for Samsung Galaxy S6 S6 Edge/Plus S7 S7 Edge S8 S8 Plus+ S9 S9 Plus S10 S10e S10 Plus - China Samsung Original Battery and Samsung