We get asked regularly for recommendations for rechargeable AA batteries for the various FoxPro units.
Personally speaking, I typically recommend the Panasonic Eneloop NiMH batteries -- particularly, the pro cell series. These can be found on Amazon or battery outlet type shops. When selecting a rechargeable battery, I almost always go with NiMH. They work very well in a wide variety of situations. The big thing to look for is the total capacity of the batteries. Most batteries today range from 2300mAh to 2800mAh and are rated at 1.2V each. The greater the capacity, the better the run time. They hold up well in colder temperatures as the chemical make up of the batteries is very different from alkaline cells. Alkaline cells have a water based electrolyte at the core and when temperatures dip to freezing and below, they can become very sluggish and fail to sustain decent operational times. NiMH batteries work on a hydrogen recombination process which is not affected nearly as much. In extreme cold (sub-zero) I recommend using lithium cells.
Here's a link to the batteries on Amazon https://www.amazon.co.uk/s/ref=nb_sb_ss_i_3_17?url=search-alias%3Daps&field-keywords=panasonic+eneloop+pro+aa&sprefix=panasonic+eneloop%2Caps%2C137&crid=194DJXIYOOFG
The Panasonic Eneloop's cost more than a lot of other types, but I believe they are a solid investment.