Good deal on getting ahold of a borrowed code-reader. You can hook up the code-reader while you drive, and see if it captures the code on the fly so to speak.

Like Oldblue mentioned, the battery could be the problem still even if it isn't very old - a bad cell can make it look marginal to the car. Most shops can do a "load test" on it to check it's health. Also, if you leave a cell phone charger or such plugged in without the engine running, it can cause the battery to wear down to the point it will cause issues.

 

My money is on the positive cable to the fuse box, or the fuse box itself.

 

I'm thinking bad ground connection somewhere.

Clare