Battery problem? in latitude e7470

Actually i bought latitude e7470 from local shop and it is used in condition,laptop is under warranty from shopkeeper as well as from DELL and everything is fine mean performance wise, but one thing which is confusing me is battery.Since i bought battery is doing strange things means it is losing it full charged capacity continuously (from 3100mwh to 1800mwh out of 4100mwh), and when i told this problem to shopkeeper he always says to discharge and charge battery from 0% to 100 %.Another strange thing is that sometime battery jumps to 6% from 27%..

So yesterday i decided to calibrate my laptop battery to 0% so when it reached 0% battery meter start showing 2 min left, but believe me i used laptop for almost 3 hour or more and then it powered off itself ,after this i recharged it all the way up to 100% but nothing changed laptop worked for only 2.5 hours,again when battery reached 7% it stuck at this point showing 14 min left but again it was at 7% for 1 hour then i powered off laptop my self.Today when i turned it on battery goes to 6% and laptop powered off ( because of the settings from "Power option").

Alright my questions are;

Why laptop battery is losing it's capacity continuously ? i know laptop battery life is only 3 years but but some laptop works fine for even 5 year.

Do you think it is related to any software changes?

Do you think latitude e7470 comes with this problem?

I have also got some "Battery report" pictures.If you need just tell me..

Thank you for reading my post.

Waiting for your reply.

Laptop specifications:

Core i5 6th gen.

Power adapter and battery both are original (asked from Dell)

Ram 8 gb.

Ssd 180gb.