Help With Diodes

[rebreok]

Hello,

I'm nearing the completion of my first portable and require assistance. You see, it was designed with battery life in mind, so I decided to wire in an external battery port for extra long car trips. However, this would obviously have to go in parallel with the internal batteries. I realized that this would present a problem, as having an external battery with a higher voltage than the internal ones would cause it to try and "charge" the internal batteries, which I don't want to happen. So, I need to place a diode between the batteries and the place where the external port connects, but I don't know the first thing about them. If you could tell me a bit about diodes, possibly even guide me towards finding the right one, I would greatly appreciate it.

Thanks,
K

 

[BtheDestroyer]

Wikipedia:

The most common function of a diode is to allow an electric current to pass in one direction (called the diode's forward direction), while blocking current in the opposite direction (the reverse direction).

Because I'm not an expert on the topic, I won't try to give any advice that may be wrong. Maybe this would work? The polarity may be off, I just did this in a few minutes...