That is not necessarily "memory". Which all majors vendors (like SAFT, who own the NiCad trademark) claim is not a problem for any major brand with new technologies for the last 20 years.
The batteries may simply be cooked, from too many hours on a cheap charger. Chargers aren't all the same, not all can be run all the time.
"Memory" is when NiCds or other cells are always cycled from full to a certain discharge level, which causes crystals or other physical changes to happen. When the same cycle is repeated often enough, those crystals (or other chemical changes) repeat and reform, reinforcing themselves at that one discharge state. To break the physical change, you need to use the batteries, full to dead and back again several times. Some will say to use a higher charge voltage as well, with time and current carefully limited.
But the bigger question may be the battery TYPE and AGE in those radios. 300 cycles may be full life for a lithium type. 500-1000 tops for NiCd and NiMh, and they won't have full power anywhere near that long. Exactly what you've got is important. If they're five years old, regardless of what they are, it would make more sense to replace them.