Question: I have a Canon SX210 IS, which doesn't have the possibility to plug-in a external power source.

Because of that, I want to make a connection to the pins where the battery usually is. I'm a little confused about the voltage requirement because the battery says 3.7V and the base of the camera says 4.2V.

Since I have a car battery and a 7805 voltage regulator I thought I could power the camera directly with the 5V the regulator would give me. But I don't know if it's safe to do that.

You may ask why would I want to power the camera with 5V instead of using 4.3 from a DC regulator. Well, I'm outside the city right now so there is no way to get a DC power supply like that.

(don't ask where I took the 7805 from).

I've found out that my helicopter charger has a voltage of 4.2V and a maximum current of 850 mA, but it's a typical switched power supply (like the cell phone ones). Is it dangerous to feed my camera with that? What about a little paralell capacitor to filter noises?

Answer: 
I looked up an SX210 manual online, and it says that there *is* an external power port. Look at page 156 of your user's manual; the online guide I found recommended the ACK-DC30 kit. You plug a coupler (which has the same form factor as a battery) into the battery bay, and plug the AC cord into a slot in the battery door. The ACK-DC30 is $50 on amazon; you can probably get an off-brand version for less, too.
Found a solution: a $5 DC to DC Converter like this

[![a $5 DC to DC Converter](https://i.stack.imgur.com/c995Z.jpg)](https://i.stack.imgur.com/c995Z.jpg)

Also you need to cut off 2 cables and remove the isolation and attach them to the DC converter.