The Li-Po battery to power the transponder must have a molex 2 pins 51005 connector:
If you need help to find compatible battery in your country, don't hesitate to ask us we'll be happy to give you links
This type of battery is very common on small drones.
The consumption of the transponder is around 20-30mA.
With 300mAh, you can expect powering the transponder for 7-8 hours
With 250mAh, you can expect powering the transponder for 6-7 hours
With 150mAh, you can expect powering the transponder for 3-4 hours
There is no Li-Po cut-off on the transponder, so check from time to time battery voltage level.
Here are some example of compatible batteries:
EU : https://hobbyking.com/en_us/turnigy-nano-tech-300mah-1s-20-40c-lipo-battery-losi-mini-compatible.html?wrh_pdp=7
150mAh and 260mAh: