Weird behavior with UBLOX neo 6M GPS

Hi guys,
I am building a robot boat using an Arduino Nano v3 and a Neo 6M gps. I am having some weird problems with reading the gps serial strings.

The gps is connected to the arduino on pins 10 and 11 (rx,tx), and I am using the SoftwareSerial library included with Arduino IDE version 1.0.6.

The GPRMC strings are handled through the TinyGPS Library.

What's weird is the software serial input doesn't function properly when using a 7.4 Lipo battery (through the onboard regulator, fed through the VIN pin), but it works fine on 5V usb power.

Any suggestions, or need any other information from me? I've tried researching the problem but can't find any help.

Thanks, Chow

How can you convince us that SoftwareSerial is the problem, when you have not stated what the problem is? Please read this before posting.