How to use device and charge their batteries when the proper accessory is lost

[Merlysys]

So many gadgets, when I need to use one the power adapter for them is often misplaced.
Not a problem for most of you as you put the gadget away in a box after using it, along with the adapter and probably the manual too!

Starting with this adapter (for SONY video camera DCR-HC21)
...what is the 3rd pin for? Any idea how to use it with just any (batteries,power supply,etc) 7.2V source?

Here is its battery, what are the middle 2 pins?

Eventually I want to build something that will enable power to any low voltage gadget and charge their batteries. Maybe there is one already I can buy, but for now I need to get this SONY working.

[MosherIV]

Hi

What 3rd pin? The cable shows the negative has a U shape metal tang.
The positive is a sinlge tang.

The easiest way is just look on Amazon with the model number and at least 2 suppliers will come up with 3rd party charger for your device.