The power board regulated and supplied power to all the other boards.  Having a separate power board enabled the creation of a common ground without the introduction of unnecessary noise, as well as an easy implementation for a kill (on/off) switch.  Five batteries were used on the COACH: two 7.2 V NiCd batteries for the bulk of the circuitry, and three 9 V batteries for those items requiring higher voltage (the E128, the music playing circuit, and the mutiny lamp.)  One 7.2 V battery powered the seven-segment displays directly, since they required greater-than-logic-level voltages and would be a significant source of current draw; the other 7.2 V battery was regulated down to 5 V to power everything else (XBee board, seven-segment display shift registers and MOSFETs, team select board, miscellaneous inputs board, and microcontroller board including encoder and potentiometer circuits.)  Both 7.2 V battery circuits had protection diodes to prevent damage in the case of the batteries being wired up with the wrong polarity.