1ST - Let you battery run DEAD on it's own. - Charge it up till the phone says it's fully charged. - Now here's were you need patience. after it's fully charged, plug it up AGAIN. IF it still says fully charged than your good to go. On mine it said fully charged but when I pluged again it continued to charge for almost 2 hours!
2ND Go to settings, internet connection, click on CONNECTIONS TAB, now edit your WIFI connection, click next, click next again, next again, now click on ADVANCE TAB, now click OTHER, on wi-fi transmission choose 10 mW. on POWER SAVING choose MAXIMUM. no click on SAVE.