From http://www.qsl.net/ka9mva/earthmate.htm
When DTR is not asserted, RING goes to 6V. When the unit is powered up (DTR high), RING goes to near 0. This is a powerup indicator.
[Lumpy from digitalcartography.com told me you can power the Earthmate from pin9. Yahoo!]

The GPS TX line is true RS232C, in the sense that it swings between -5V and 5V.

The Earthmate is powered by four AAA batteries, nominally 6VDC. My unit only pulls 85 mA at 6.0VDC. This is extremely low, and can be supplied from a 78L06 regulator easily.

When my unit is powered down (DTR=0), it pulls around 125 uA (yes, that's microamperes).

I think this means that I can send 6 volts to pin 9 (negative I assume) instead of using the battery? But which pin to I connect the positive wire to, pin 4?