Replaced the original 7 year old battery in my key fob. No big deal, should take about 2 minutes to do but I'm old and need directions. This video helped.
Mine takes a CR2016 battery. If you have a dollar store close by you can pick it up cheap. I got 2 for $1. at the Dollar Tree.
A bit of trivia. What does fob mean?
https://www.quora.com/What-does-fob-mean-as-in-key-fob