Welcome seatosea.
Cradles can be a problem. But, if the AX has a connector problem a new cradle won't make any difference. I've had one cradle go bad, but it was the chip in it and not the connector. I also have one AX with the connector problem and one that does not.
Remember too, the x51 doesn't have a backup
battery. It's a capacitor. If you have the battery used in the x50 models, it won't work in the x51.
Ps - Here's a link to changing the capacitor:
Replacing the back-up battery in an Axim X51V