Re: portable controls w/o using tether
 

If you do this, you'll need to limit the current flowing into the battery pack, otherwise you could damage it.
Otherwise it would be totaly possible to do. Just use 2 schottky diodes that can handle the current into and out of the battery, and a resistor on the one that will be used during charging. That will make sure you have enough current to power the OI, but don't toast the battery.

Re: portable controls w/o using tether
 

Attached is the OI power system the captain and I made. It has a wall jack for 9v input and the transfer switch is near by. in the lower right corner, three 9v batteries are visible. In my previous post, I mentioned that I was making another one. It's still under construction because I discovered the charge controller I was going to use from a backup battery charger wasn't in use for a good reason (It smelled like a burnt victor and, upon further inspection, I discovered one of the IC's had violently lost half it's mass at some point).

Re: protable controls w/o using teather
 

WHOAOAOA!!! The picture (discussed about 1 post below yours) has 3 9v batteries!!! Can the OI safely work on 3batt * 9v = 27volts? Just curious :D

Re: portable controls w/o using tether
 

The 7.2v backup battery works just fine.

"I know, I've seen me do it"

If you are planning on a very long presentation or something of that matter, wire up a simple bus to connect 2 or 4 in parallel. The gentleman from IFI used just one when running diagnostics on peoples robots at our regional in Detroit.

Re: protable controls w/o using teather
 

Those batteries are running in parallel, not series. Therefore, the voltage is still 9v. This is done to increase capacity, or, run time of the OI while being run on batteries.

Re: portable controls w/o using tether
 

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.

Re: portable controls w/o using tether
 

I'll second what Al has said, and note that the manuals indicate that the only approved adapter on the power port for the OI is the power adapter that is provided in the kit. If you make a mistake hacking the power for the OI, your OI will escape its warranty.

If you want the convenience of live charging for a battery operated OI, and the lack of risk that providing a regulated supply for the correct voltage to the OI gives, you need to be meticulous in how you do it.
You need to use a battery technology, and charger, that does not induce pulses on the power line, and Al has pointed out the risks of how NiCd chargers normally work on this front.
Your best choice is a lead acid gel battery of a suitable size, and these are likely to come as 12 volt units. I would not apply 12 volts directly to a power port that is normally operated by a 9 volt source. You could swamp the power dissipation capability of any internal voltage regulator in the OI if it is not designed for it. I have not seen technical specifications for the OI that indicate that the power port is designed for handling more voltage, and do see a specific caution with regard to using only the provided power cube on this port.
So, what to do, if you really want the "cool" capability of an OI that can stay live while you connect and disconnect the power line? You need to use a 12 volt gel cell that can handle the current requirements while not being so large that portability is hurt. The 12 volt battery used in the old analog "bag" cell phones is a likely candiate, but you can probably find others. You need to build a voltage regulator that can drop this supply to the voltage required by the OI, the LM350T could be used to get the job done. Measure the current draw from the power port and use that to figure out how much power your voltage regulator must shed as heat. Use an appropriate heat sink and an appropriate insulating mounting for the regulator on the heat sink. Finally, find a battery charger for your chosen battery that is reasonably well regulated, minimizing any ac hum induced on the battery.
It takes a relatively minor engineering effort to put it all together, but you will end up with a useful capability that you would be proud of and the excercise is educational.

Remember, your OI warranty will be voided, but that is often the price of having fun...

Re: portable controls w/o using tether
 

2 6v lantern batteries... large, but by no means heavy like a SLA, and easy to find. or 9.6v battery packs, like mentioned earlier.

Or you can make a mini trailer for the robot and have your operator crouch on that with the controls, tethered to the robot, as it pulls the trailer. :D