Loose XM antenna connection for garmin 2730

You indicated that the battery went dead. Does the new battery work correctly? That is, does it show a full charge when you've had it plugged in overnight and disconnect the power? Try plugging it into AC power overnight and verify that the battery is accepting and holding a full charge. If it isn't, then unplug and turn the unit on and allow the battery to run all the way down. Then charge it fully. This resets the charge indicator. You may have to repeat it once. I did this and was able to again show that both my new and my old battery were working o.k. They should show about 8.1 V fully charged.
About the Nexrad problem. In the past I would need to refresh the XM receiver when this happened. XM walked me through it and I have the steps, but the links are no longer working. Maybe it is no longer required since the XM link now jumps to SiriusXM. I've not needed to refresh for a couple of years and I suspect they eliminated that requirement.
To verify that the XM antenna is connected: Turn unit off. Connect the XM receiver. Simultaneously press "on" and "enter" keys- hold both until data screen appears, which takes about 5 seconds. Second line from bottom indicates if it is seeing the XM receiver. This helps isolate where the problem is- i.e. if you have a faulty receiver, bad connection or a software problem. The only contact I know of now is Garmin 800-800-1020. They can give you the XM contact if the problem is on that side of the unit. There is other data here which may be of interest to you on this page. Turn unit off to close this window.
If you need your XM radio ID, turn 396 on. Press menu, menu, scroll to XM, then right to Info. XM Receiver ID is there. Write it down in case you talk to XM or they give you a way to refresh. There are other menus you can get into but if they show a problem I don't know the solution other than contacting Garmin and I don't have my XM receiver home so can't verify the steps.

To receive XM weather or audio, the GPSMAP 740s requires a GXM 40 Smart Antenna with XM subscription.

The GXM 40 Smart Antenna (010-00730-00) is used to receive weather and audio service from XM satellite radio. For details on XM services please visit our XM webpage.

Once a GXM 40 Smart Antenna has been connected to the GPSMAP 640, the device can display the subscription information for the antenna.

From the Home Page in Boating mode:

1. Select Configure
2. Select System
3. Select System Information
4. Choose Weather Subscription

From the Home Page in Driving mode:

1. Select Tools
2. Select XM Services
3. Select XM Radio
4. Set the channel selector to channel 0
5. Select Radio ID

The subscription information will now be displayed on the screen.

DIY is risky in this situation, besides there is 3 months warranty by Garmin on their interventions I would suggest you get it done by the professionals

You begin by setting up your existing (((XM))) antenna the one that came in your home kit (not included in repeater package) in a location that gets good reception of the (((XM))) signal. This may be outside, or on a south facing window sill. This antenna gets plugged into the rear of the Delphi (((XM))) Radio Signal Repeater Transmitter. A power jack is right next to the antenna connection, and should be plugged in and to the wall with the included power supply. There is also a "PWR OUT" selector switch on the rear of the unit which allows you to control the strength of the signal transmitted from the unit.

Once the power and antenna are attached, both blue indicator lights will light up on the face of the unit. The blue antenna indicator will light up only to signify that the antenna is attached correctly. It does not let you know whether your antenna is in a location receiving a good (((XM))) signal or not. You will have to look at the signal strength indicator on your (((XM))) radio receiver do determine best location for the (((XM))) antenna.

Once you have this setup, place the Repeater Antenna close to your existing (((XM))) Radio and plug it into your antenna jack on the (((XM))) radio cradle. This connector is identical to your (((XM))) Home Antenna provided with all Boom boxes and (((XM))) home receivers and kits so compatibility is guaranteed. The Repeater Receiver Antenna does not require any separate power connections. Hope this helps!
SATELLITE RADIO WAREHOUSE

Did you try cleaning the output jack with a q-tip and alcohol? Otherwise you might have to send the unit to garmin if it is worth it to you.

Do a hard reset.

Turn the unit off, then hold down the menu and map buttons, simultaneously, then turn the unit back on and continue to hold down the buttons down for at least five more seconds, then the unit will power up. At that point it's like the unit is being used for the first time and you will have to reset everything. You will lose your XM presets, but the MP3's were still there.

Also after if this does not work, plug in your garmin and mount it, mac or pc whatever, then go in your garmin file erase all maps should be gmapsupp.img or gmapprom.img. Reload your maps from mapinstall.

Try with a different XM Antenna from a friend or shop if possible to verify whether it's the antenna or the unit itself.
Visually inspect antenna cable and connection at the antenna and the unit and make sure the antenna cable hasn't been damaged.
I would do this before considering other options
Good Luck!

The GPS is defective. Your usb/xm port is broken. You need to send it back to garmin.

if the xm and gps antennas are close together this will happen. u will have to move one to the front and the other to the back of the vehicle.

try to change the antenna