can I run a 6 volt motor with a 7.2 or 9.6 volt battery pack?

You could be in trouble if:

1) The tool has an integrated charging system 2) There is ancillary control circuitry in the tool that could be damaged by the higher voltage 3) The physical attachment of the battery pack to the tool is not compatable in which case there could be a tangled wires safety issue 4) If the tool incorporates a gear reduction mechanism and the increased voltage elevates the available torque to the point that the tool could rip itself from your grip. 5) Certain tool attachments may not stand up to increased torque or speed and lead to unsafe broken tool parts.

Another safety concern is the total battery capacity and short circuit current draw available from the pack. If the original pack has lower capacity then the increased capacity of the alternate pack could severely increase the range over which the tool keeps going when you expose the motor to near stall conditions (see 4 above in particular). If the new pack has too low of capacity then a heavy usage load of the tool could put so much current draw load on the new battery pack so as to increase temperature rise and cause potential fire or explosion.

- mkaras

Itl live fast but die young. I do this with some motors, I find the bushes dont last long at all, so I replace them with ball bearings.

Colin =^.^=

it will shorten its life (possibly not significantly), and may damage the electronics that control the motor speed/torque (which will shorten its life dramatically).

cordless tools are often underpowered compared to mains powered tools, if you want more 'go' build an inverter belt!

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Bye.
   Jasen