Some examples of collar transmitters with only one single battery up to 7 batteries with internal and external antennas, changeable batteries and expanding capability

L - 1 / ER3 [I]

On the left or above,
one ER3 batt. with internal antenna, weight approx. 30g for, marten and comparable.

L -  1 / ER3 [I, W] 

On the left or above,
one ER3 batt. internal antenna and changeable 1 Ah battery, weight 70g here used for ozelots.