There isn't any battery in the antenna but there are a lot of electronics in the antenna that get powered from the Tivoli radio over the antenna's coax cable. Most likely the antenna's cable has been disconnected or severed or the electronics inside the antenna have failed. You mention the antenna is mounted outside so if it is located more than 20 feet from the tivoli radio, then your installation uses an extension coaxial cable so you should check to see if the cable has become disconnected or unplugged from the Tivoli radio or: follow the cable from back of the Tivoli radio all the way to the antenna to see if it has become broken or disconnected. Often these cables break where they transit from inside the home to outside. They might get pinched by a window for example. The antenna or any extension cable might be broken and need to be replaced. Our latest antenna is the NGHA3 available from BestBuy here: https://www.bestbuy.com/site/searchpage.jsp?st=NGHA3&_dyncharset=UTF-8&_dynSessConf=&id=pcat17071&type=page&sc=Global&cp=1&nrp=&sp=&qp=&list=n&af=true&iht=y&usc=All+Categories&ks=960&keys=keys
and the antenna extension cables are available on SXM's website: https://shop.siriusxm.com/50ft-home-antenna-extension.html.

Note: it is also possible that the Tivoli radio is broken so if you purchase a new antenna first just plug the antenna directly to the Tivoli radio before installing it. If connecting a new antenna to the Tivoli makes the "antenna not detected" message go away that will confirm the Tivoli is OK. If the error message remains then your Tivoli radio has failed. The new antenna must be mounted outside for proper reception but trying the new antenna indoor as described above is an easy temporary test to rule out the Tivoli as a cause of failure.

Yes, this will work very well with your Ford's FM radio. With the FM Direct Adapter (FMDA25) installed the FMDA25 connects in-line with the FM radio's antenna. When you turn on your SXM Radio, the FMDA25 will interrupt the connection from the external vehicle FM Antenna and route the FM modulator signal from your SXM radio to your vehicle's FM radio. This will completely eliminate all external interference from all broadcast FM stations while allowing clear reception of the satellite audio from the SXM radio. Just set a preset on you FM radio to match the frequency set on your SXM radio's built in FM modulator and when you turn on the SXM Radio the FMDA25 will automatically route the SXM's FM signal to the car stereo and when you turn off the SXM radio the FMDA25 will automatically reconnect the vehicle's FM antenna for normal FM broadcast reception.

If your car stereo includes an Auxiliary input then your Onyx Plus includes the 3.5mm stereo cable to directly connect to your car stereo. If you car stereo does not have an Aux-input then the best option is to use the FM direct Adapter (FMDA25). The Onyx Plus has a built in FM Modulator and the FMDA25 will connect the FM modulator directly to your car stereo and the FMDA25 will eliminate all interference while listening to the Onyx Plus on FM. Then when you turn off the Onyx Plus normal broadcast FM reception is automatically restored. We recommend professional installation as the FMDA25 needs to be installed at the FM antenna cable at the back of your car stereo. This is the link to the FM adapter at BestBuy and BestBuy can arrange installation as well for an additional fee: https://www.bestbuy.com/site/siriusxm-fm-direct-adapter-black/8116585.p?skuId=8116585

Yes, the NGHA3 SXM Home antenna is compatible with the SUBX2.