Two way radios use several types of battery technologies. Some two-way radios take standard AA batteries that allow you to use rechargeable batteries, but in event of a long power outage, you can use off the shelf AA batteries when your rechargeable batteries die. Other radios use a custom size battery. For these you can purchase spare batteries that you can have charged and ready to go in the event your primary battery charge runs out. Two-way radios come with a charger unit to keep the primary batteries charged, and in the case of custom batteries, they usually include a slot for the backup battery too.
There are three types of batteries that are typically used for rechargeable two-way radios: nickel cadmium (NiCAD), nickel metal hydride (NiMH), and lithium ion (LiION). You cant typically choose the type of battery you use for most two-way radios. The manufacturer does that for you. Following are some of the advantages and disadvantages of each type.
Good at low temperatures, resistant to overcharging, long life expectancy, low cost.
Larger and heavier, memory effect reduces effectiveness if not fully discharged,
No memory effect, lighter than NiCAD
Shorter life expectancy, special charger required to limit overcharging.
Fast charging, no memory effect, slow loss of charge when not in use, lighter than other batteries.
Higher cost, after a number of maximum number of charges they no longer accept a charge (typically 500 to 1000).