Lower-end FRS/GMRS walkie-talkies might use AA or AAA batteries, but most two-way radios use one of 3 types of batteries: NiCad, NiMH or Li-Ion.
Ni-Cad or nickel-cadmium batteries have been around the longest. They have a long life expectancy and are less prone to the problems associated with overcharging. They are the cheapest battery chemistry of the three. However, they are also the heaviest and tend to be susceptible to 'memory burn.'
Memory Burn occurs when a battery is recharged before it's fully discharged. The battery will 'remember' the partial charge and only fill up that far the next time it is being recharged. This shortens the power potential of the battery to that smaller, partial amount. To avoid memory burn, it's best to fully discharge your batteries before recharging them. If proper care is taken, Ni-Cad batteries can last 2-3 years.
Nickel Metal Hydride batteries share some chemistry with Ni-Cad batteries, but don't share their vulnerability to memory burn. Nickel Metal Hydride batteries are a bit more expensive and are more susceptible to overcharging issues, but they are smaller and lighter. They typically last 1-2 years.
Li-Ion batteries are the most expensive of the three. They don't get memory burn and are the smallest and lightest of the bunch. However, they are limited to a specific number of charging cycles and once that number is reached (500, 750, 1000) they won't take another charge. Also, their advanced chemistry means they require a special type of charger, but it can have them up and running in as little as an hour. Batteries are built on a basic calculation of 5/5/90. Battery manufacturers assume the battery will have a duty cycle of 5% talk-time, 5% listening time, 90% standby. References you may see as to the battery duration of X number of hours are typically based on the 5/5/90 assumed usage.