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:
Hobbyking:

300mAh : https://hobbyking.com/fr_fr/turnigy-nano-tech-300mah-1s-20-40c-lipo-pack-losi-mini-compatible.html

260mAh : https://hobbyking.com/fr_fr/turnigy-nano-tech-260mah-1s-35-70c-lipo-pack-qr-ladybird-genius-cp-mini-cp.html

France:

300mAh : https://www.amazon.fr/dp/B01A6O786S/ref=pe_386181_40444391_TE_item 

250mAh: https://www.amazon.fr/dp/B01A6O786S/ref=pd_luc_rh_sbs_01_01_t_img_lh

150mAh: https://www.amazon.fr/gp/product/B06XB6WTGQ/ref=ox_sc_act_title_1

US:

250mAh: https://www.amazon.com/BTG-250mah-Battery-Charger-Ladybird/dp/B0122OZJ0W

China:

150mAh and 260mAh: banggood

150mAh: aliexpress

260mah: aliexpress