Found a video showing were it should be. I am going to check it now.

Will this battery being bad cause the truck to not start?

 

Just check, no battery in that spot on my truck.

 

The second small battery if you have one is for the auto stop start. Without it or if it's aged the car will still start and run but you might get an error in the info section on the dash.

 

Just had the sane issue with a 2016 LR4. Auxiliary battery was dead but i didn't replace it (because ECO feature was disabled), but then main battery died and a jump start would not work. I had to have it towed to the dealer. Good news, Batteries were all covered under the bumper to bumper warranty (50k miles or 4 years).