Batteries
Almost all combat robots are powered by batteries. Although compressed gas or internal combustion engines are occasionally used (especially for weapons), batteries are always required.
There are too many batteries to choose from to make any meaningful list here, so we list some criteria to consider when choosing a battery.
Battery types (chemistry)
Nowadays (2021) nearly all combat robots run on lithium polymer (LiPo) battery packs. This is because they give the highest power density and are widely available. For safety, childrens' toy robots usually use a different type, generally NiMH. Transmitters often use other types.
Series and parallel cells
Battery packs are generally formed of more than one "cell". These are put in series or occasionally parallel.
Series cells = more volts Parallel cells = more amps
Be careful with series or parallel cells - it is usually better to buy a ready made pack with the correct number / size of cells.
How much capacity do I need?
Chargers
Safety
Connectors
There are too many annoying connector types which aren't compatible :) we could put a picture of some of them here.