I've got an s6 edge which is about 3 years old now and i just installed a brand new battery, its an original from samsung and there's written 2600mah on it, but when measuring the mah with accubattery it shows around 1600mah estimated capacity, the battery feels longer but i'm not sure what to think anymore, i fully discharged and charged overnight.
Read more: https://samsungus.org/qa/s6/new-battery-shows-lower-capacity.html