My be your 3g modem drains a lot of battery and your router's battery is not capable of supplying it. That is it works when you connect it to charger. Hope it helps Furqan.

Region : Argentina Model : TL-MR3220 Hardware Version : V2 Firmware Version : ISP : =My tp-link mr3040 behaving abnormally. It was working perfectly normal when I bought it but now about 2 week later...