Many years ago, when my kids were young and I was a registered Girl Scout leader, I would accompany my daughter's troop when it involved the outdoors* (hiking, camping, ...).

I once offered to give an explanation/demonstration of how a GPS works and how to use a handheld GPS. Sure enough, I'd forgotten to precheck the batteries, they died within the first 5 minutes, and I failed to bring extra batteries. It was mighty embarrassing to have to borrow batteries from one of the girls.

Ever since then I am a fanatic about bringing extra - and too many - batteries, so I appreciate battery holders.

*Sadly, the Girl Scout parents assumed all fathers who wished to volunteer were sex offenders. The founder of my daughter's troop was an amazing man, who was rapidly forced out by the parents and replaced by an equally amazing woman who was also an Assistant Scoutmaster in my son's Boy Scout troop. I'm happy to say it was just the opposite with my son's Boy Scout troop. Woman leader were very welcome.