DataLogging with Arduino UNO: Won't work independent of computer

Other Hardware Storage
1

I'm using an Uno with a sensor and microSD Shield to store data to an SD card. Everything works fine when it is connected to the computer, but when I try to run it with a battery power supply, nothing is written to the card. Also, when I try the same code on an Arduino Mega, everything works fine independent of the computer. Any ideas on why it wouldn't work for the Uno?

Here is the Shield I'm using:

2

check it with a multimeter.
What is the voltage between the pind GND and Vin?
What is the voltage between the pins GND and 5V?
What is the voltage of your batteries?

3

I have similar problem with UNO.
try this.

  1. power on
  2. push reset button.
    In my case, if I do this, de UNO work correctly, but need make reset after power on. I don't undestand this but...