why does my android S4 show only 2 bars when the router is working fine at full strength?

[Sharon]

I have 70% battery left

 

[B. Diddy]

Welcome to Android Central! Wi-fi signal strength can be affected by how congested that wi-fi channel is (from networks around you). Use an app like Wi-fi Analyzer to see if the channel your router is using is particularly congested. If so, then change the wi-fi channel on the router's settings (see the router's manual to learn how to do that).