I am being experiencing this very strange issue in the last couple days. I have a Samsung Galaxy S3 Mini with an (unofficial) build of Cyanogenmod 11. Is has been working fine for the last year with this ROM. However, since yesterday, the WiFi is not working very well.
Basically, when I turn it on, it doesn't find all the networks I expect. When I connect to my home network, it shows a very weak signal and often disconnects completely.
Another issue that I think could be related to, is the battery. It discharges very quickly, I need to charge the phone twice a day (it's not a big problem though). Sometimes if I reboot the phone, I loose up to 30% of charge.
After various test, I found out that when the battery is very low, the WiFi scans but doesn't find any network, hence I can't use it. When the battery is half charged, I can connect to my network, but the connection is very unstable. When it's fully charged, I can connect to my network and browse the web normally.
Now the weird part is, if I plug my phone to AC power, the connection is (almost) perfect. WiFi works, it finds all the networks, and the signal is great.
If I try pinging
184.108.40.206 from the phone on half battery, I get several packet drops with time ranging from 200ms to 10000ms. On AC power, it is mostly stable on 40ms. All this problems are identical with another network.
I would like to know if the battery and the WiFi issues are related?