Size of Battery

How to choose the right size of battery
As mentioned earlier, batteries come in all shapes and size, from types no larger than a shirt button, to a battery system filling an entire room.
To find the size of battery you require you generally need two pieces of information, battery load and back-up times. (Note: other factors may also have an effect).

Battery Load
Whether you power lights, motors, electronic equipment or a toy vehicle you equipment will draw a load in AMPS. If this is unknown then the equipment will have a rating expressed in Watts which may simply be converted to Amps by dividing the value by the normal voltage of the system.