[Al Skierkiewicz]

Ok,
I do have to jump in here and say something. Putting batteries in parallel without some protection is a bad idea. The higher voltage battery will try to pump current into the lower voltage battery to equalize the voltage and the cycle will continue until the batteries all discharge. A diode is needed to prevent each battery from supplying current to the other battery. With small batteries this effect may be unnoticed, but it is still taking place. It is a simple matter to buy a 12 volt battery holder (from Radio Shack) and fill it with D cell alkalines and get a 12 volt source with plenty of current. Be sure to watch the polarity of the battery connector so you don't reverse the voltage into the OI.
It is never a good idea to use a charger as a voltage source for the OI. Many chargers, especially NiCad chargers use a pulse method of charging and the peak of the pulse can exceed 12 volts by a considerable amount. Either use a standard 12 vot power supply (regulated please) or a battery. Your OI thanks you, your team thanks you and I thank you.