If yours doesn’t have the AA cell holder then it needs a 2-4s lipo receiver pack. Measure the size of the battery compartment and get a pack a couple of MM smaller in each dimension. I would go with a 2s lipo or 3s LifePo4 pack for best fit. If you use a lipo always unplug it after use and check the cell voltage regularly.
Some pictures half way down the page here of the AA holder. https://www.rcgeeks.co.uk/blog/radiolink-transmitter-receiver-range