Harleyguy

Should be able to get them at Walmart, K-Mart, Ace Hardware, any auto parts store.Just match the number stamped on the old battery, in this case a CR1620. Should be able to pop them right in per the owners manual instructions. RossTech essentially is a cable that you purchase to connect a lap top to your car and you down load their software from the internet. Based on what I have heard here on your post DO NOT BUY THIS and try to use it yourself. You do not appear to have the knowledge and background. Try the battery in the fob first and see what happens.

meternerd

Does the key fob lock and unlock the doors? If it was the key fob battery, it shouldn't have enough power to lock and unlock the doors, let alone allow it to start. The fact that the lights come on when you turn on the key and it runs OK when it does start and the problem is intermittent sounds like a bad ignition switch, relay or loose/poor connector. It may also be the neutral/park switch. Try moving the shifter (if it's an automatic) with your foot on the brake while you're holding the key in the start position and see if anything happens. Codes need to be reset, then see which ones come back, (if you can get it to start). Could be old ones that don't auto-reset. Any Auto Zone or others can at least reset your "check engine" light for free. Just some things I'd try before buying any more parts.