GPRS shield RF interference

I have a project that reads RF tags and then on a daily basis sends information on the tags to a user via a txt message. However i have been having issues with, I suspect, rf interference on the supply DC lines to an arduino UNO and the reader. The GPRS shield is version two and this is plugged into a arduino UNO R3 and a logging shield (adafruit) is also plugged into it.

If i run the UNO and the RFID redaer (with rs232 output) from the same battery supply, the reader stops working or works for a bit but does not read tags. If if run the UNO from a separate supply everything seems to work fine. However if i remove the GPRS shield and run the uno+logging shield from the same battery supply as the readaer everything works fine. It seems to be the addition of the GPRS shield that causes the problem.

Any ideas what could be gong on here.

Any help is much appreciated.