I'm sure this topic has been discussed in the past, however in doing a search I cannot find the "why" behind disconnecting the negative cable from the the battery helps a key fob that has new batteries in it...

After trying and re-trying several times to get my spare key fob (with a set of brand new batteries installed) to correspond with the car it seems that the very last thing to try before going to a dealership is to disconnect the negative cable on the battery.

How does that help to re-program the fob? Also, would'nt that erase the other fob i have thats working?

Thank you all in advance!