Batteries

The following table lists some typical characteristics of the most popular types of batteries:

	Alkaline	NiCad	NiMH	unit
Cell Voltage	1.5	1.2	1.2	volt
Capacity	2000	500	1100	mAh
Energy Density	190	44	53	Wh/kg
Internal Resistance	150	10	30	mohm
Charger	none	simple	harder

 

Alkaline: These are readily available at any store and they provide a higher cell voltage than the rechargeable cells. Because of their high internal resistance, however, they cannot provide the current needed by power-hungry motors.

NiCad: These have a lower cell voltage so you will need more cells to achieve a given voltage. They are easy to recharge, however, and because of their low internal resistance will provide the surges of current needed to drive a motor. This is why they are common in cordless power tools and in the high-performance mice.

NiMH: Although they are trickier to charge than the NiCads, the NiMH have twice the energy capacity and will drive your robot twice as long.

 

Summary

With the popularity of digital cameras, NiMH batteries and their chargers have become common and their prices have come down. Of the three types of cells, NiMH are the best compromise between performance and energy capacity.

You might also want to add a DC jack to your mouse so that you can run it from a power supply during development.