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Originally Posted by Al Skierkiewicz
Ok,
Putting batteries in parallel without some protection is a bad idea...
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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...