Instead of using the battery solution, try one of these:
http://www.zytrax.com/tech/layer_1/cables/heavy.htm
The reason it may not be working is that the Axim requires RTS and CTS to be high, or it also requires the DSR, DCD, and DTR to be high as well.
Chances are that the device you are trying to connect to only supports tx, rx, and gnd. This is certainly the case on other devices with simple serial interfaces like Garmin GPS devices.
Cheers
(Remember you are responsible for your own actions :crooked: )