I have an AFS 5500 touchscreen EFIS set up with the Skyview network. Like my Garmin G5 backup EFIS and the Garmin Aera 660 backup GPS I would like to install a backup battery for the EFIS. The Garmin G5 has an attached backup battery the and Aera 660 GPS has a built in Battery, both charged by the Acft electrical system. I have a TCW backup battery for the avionics stack but would like a separate backup EFIS battery setup similar to the way Garmin does it. Is there a backup battery that mounts onto the back of the 5500 EFIS? If not, why not? Doesn’t seem like much a problem for the smart guys at AFS.......