Have a 2018 Honda CRV and the battery died.

I've heard of a separate battery hooked to the starter feed beneath the car with the neg. on a ground .

Hello Guru91RZRV, Wow, I wish I had an answer for you but I don't. Hope you will follow-up and let the community know how you get this resolved and specifically why your key wouldn't work.. As the owner of a 2018, the first thing I did was pull my key from the fob and go outside with only the key and give it a try. It worked once I got it in right but I don't have a dead battery. My presumption was that the key unlocked the door in classic mechanical fashion and electricity wasn't involved but given the the firm click (thunk) of the lock releasing and flashing lights, I'm not so sure the unlock wasn't electrically activated. Your comment "By the time I went to work on it" would lead me to suspect the battery had been 'dead' for some extended period of time and been drained dead dead by all the car's systems that suck electricity 24/7.