The TX comes with a charging equipment - A charging lead + USB cable.
Per the manual - There will be a red light on the charging lead while the TX is getting charged. Once done it will be green.

My story
I connected the USB cable to my laptop on one end and charging lead on the other. The light was already green when i did that. I then connected the TX and the light went off. Kept the TX on charge overnight(just incase the indicators were faulty) but no results.

Everything i am using is stock. Anyone who has faced a similar issue or can help.

The usb port of a laptop can provide only 300ma but the graupner battery requires 700-800ma current to charge  so try using a mobile charger with usb port(like nexus charger) or a power bank...which can deliver more current

Most of the USB 2 ports are up to 450 ma & USB 3 are 1A now.

Tried using the mobile charger with USB port,yet it won't charge :-(