once paired, a BT device like a radio should remember the pairing, as should your phone.
with my pioneer car stereos, you have to go into the menu, find 'phone connect', and do a dance where you set your phone to be listening for new devices, then choose phone connect on the stereo, and accept the pairing when it assks you if the code is OK. but once you've done this it remembers it, even if the power is disconnected entirely.
2014 Escape 21 (home away from home)
2002 Ford F250 7.3 Diesel 4x4 (tug)
1993 Mercedes 300CE Cabriolet (daily driver)
2006 Yellow Lab (Maggie... RIP Feb 2019