I think the proximity key sensors for the push-start and door locks draw a lot more battery power than old lock/unlock/panic fobs. Had the first low key battery warning in 2020 on my 2019 model, and since I've gone through another battery but it was based on how close I need to put my pocket up to the rear hatch to get it to unlock and open on proximity.
Re: using the spare key.. depending on how close the main key was it may have still detected it and the low battery - hanging on the wall of the garage 5 feet away? Or the spare may also be low. Could try moving it further away or see if the warning comes up with the spare when you start up at the grocery store.
The fob is easy to split open and swap in a new 2032 cell. Find a multipack on Amazon of a decent brand for $2-3/cell. I keep one in the center console - my fob has a removable door key, so I can always get in and get to the backup battery if its fully toast, but I think the manual even states to use the fob to push the start button if its real close to dead.
Re: using the spare key.. depending on how close the main key was it may have still detected it and the low battery - hanging on the wall of the garage 5 feet away? Or the spare may also be low. Could try moving it further away or see if the warning comes up with the spare when you start up at the grocery store.
The fob is easy to split open and swap in a new 2032 cell. Find a multipack on Amazon of a decent brand for $2-3/cell. I keep one in the center console - my fob has a removable door key, so I can always get in and get to the backup battery if its fully toast, but I think the manual even states to use the fob to push the start button if its real close to dead.
