Problem after update to ios 11.3.1

Hello! I'm having a problem with the battery when I switch from ios 11.2.6 to 11.3.1 on my iphone 6s.

Initially, my battery showed was original and factory. I updated the software, and I started having problems. in the settings, the battery wear was shown as small (93% capacity), but suddenly the phone began to discharge quickly,

show incorrect charge. Deciding that the case in the battery, replaced it with a new one. Now I have a 100% battery, but the work time has not improved. After a while, I stopped showing usage statistics.

Perhaps my battery is not original(Unfortunately, in my country there is no apple store, and I can not get authorized repair of apple), but can there be a problem with my old battery,

which had a capacity of 93%? The phone could shut down, start suddenly discharging by interest in a few seconds, and after a hard reboot, show different charge values. At 11.2.6 this was not! Can there be problems in the software itself?