This Instructable will show you how to work around a proprietary or a non-existent power connector by making a battery substitute power connector that will allow an external power source to be used.
Step 1: The power supply
In many devices, such as a flashlight, the batteries are wired in series. In these devices you may be able to combine the voltages with a single battery substitute connector and power supply that provides only the total voltage, hence one AA = 1.5 votls, so 2 x AA = 3 volts..
In other, more sophisticated devices like cameras the batteries may be wired, or look like they are wired, in series but the series connection between them may be tapped or non-existent. If you are making a battery substitute power connector for one of these devices then you might have to make separate 1.5 volt battery substitute connectors and supplies for each battery the device will use.
External Power Sources
A portable external power supply can be made using a bank of external cells wired in parallel to keep your device going all day.
If you don't need portability as with studio type work a wall wort type power adapter with a minimum rating of 1 amp can be made using a transformer, bridge rectifier and a voltage regulator. Most regulators will handle a supply of up to 36 volts so a wide range of transformers can be used. A large micro farad capacitor with various other circuit refinements can be incorporated to provide power that is smooth. A circuit diagram based on the 78xx voltage regulator series is shown below.
The other options are to purchase a used 1.5 or 3 volts power adapter at a thrift store or a new one from Radio Shack or Wal-Mart for a little more cash. Multiple output voltage adapters, if they have a 1.5 or a 3 volt output, can be used as well but may be more expensive. Be sure you have one that is rated for at least 1 amp output. Otherwise your device will probably not operate or will at some point do the very thing you are trying to over come, which is to shutdown.
I opted for a wall wort type power supply from Radio Shack because one was sitting in my drawer. (Its only rated at .3 amps so I replaced it with a bigger one.)