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.

Roger's Hobby Center has a really good guide to lipo batteries.

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?

Since keeping your robots weight down is always a high priority, you should only use as much battery as you need. One of the best tools for this was created by the legendary Steve Judd of Team Tentacle. His amp hour calculator helps determine how much battery you'll need for your robot's drive system. Team Run Amok hosts a version of the calculator over on their Ask Aaron site that you can use.
Don't worry if the calculator doesn't list your chosen motor. You can still get a good estimate of how much capacity you need by typing in the proper voltage, weight, wheel speed and size into the calculator. The Ask Aaron site does a good job explaining how the calculator works.
Once you've figured out what you need for your drive system, you'll need to also add in the capacity you'll need for your weapon system.

Safety

See Roger's Hobby center (link above). Rules of thumb:

• Use the right charger type (and settings)
• Don't use parallel charging boards
• Charge in a lipo bag
• discard damaged / puffy packs

Connectors

There are too many annoying connector types which aren't compatible :) we could put a picture of some of them here.