Walkie-talkie radios generally have a detachable re-chargeable battery pack on the back, usually Lithium-Ion, although some are Nickel Metal Hydridge.
All rechargeable batteries cannot be charged and discharged indefinitely – they gradually lose capacity.
On most of the walkie talkie radios that we sell, the batteries should last 400 to 500 full charges and discharges.
During this time, the capacity and therefore the number of hours that you can use the walkie-talkie between battery charges will decrease.