Samsung Galaxy S3 WIFI trouble-always says "not in range" NO SIGNAL

I don't know if this is a lame problem compared to others here. But this is the only way I know I can get help from.

My brother gave me his S3 this 2015, and I think the phone is about 2 years old. It's been working fine, although I didn't put any SIM to it, it's mostly for internet use specifically watching YouTube videos using home wifi. This device made me happy.

Until recently, I tried charging the phone (with earphones on), and when it reached 70%, I unplugged and stopped the charging for a while. After a few hours, I resumed the charging again up to 100%. That's the time I found out I cannot surf YouTube anymore or Google or Skype etc. I went to Settings and checked the Wifi connection, and it says "not in range". I checked another cellphone and the home Wifi is working there, so the router is not the problem. I also tried removing the battery, and putting it back on after 1 minute (of course shutting down the phone), but still no Wifi. I also noticed that the battery doesn't lose life easily or the percentage number deducts in a very slow manner, compared to its usual charged state before that loses power/percentage in a faster pace.

Is it overcharging, do you think? I tried restarting but it's still the same. I hope somebody out there can give me simple solutions, please make the language simple as I am not a techie. Only simple and clear language please. Thanks!