I was at either Canadian Tire or Walmart when I saw about a year ago a dual battery charger. I read the box and it said that once one battery is fully charged, it redirects the current to the other battery.

I thought to myself, man this is neat, when I get all my hardware, I will definitely buy this.

Well, I've got all the hardware (CPU and Lilliput screen), and now I need to put a second battery in my car, and I want the alternator to charge my main battery first all the time.

I can't remember where I saw this because neither carries them anymore. Can someone tell me a website, or what these "DUAL CHARGE SPLITTERS" are actually called to I can properly ask around in stores or check ebay?