Also including how to get 18650 batteries to fit, that are just that bit taller.
Good catch, Mark, with that little piece of material being the only thing in the way. Think they would have tried putting batteries in the thing before putting on the market!
That was a great catch @EatMaBB.
It will depend on what manufacturers batteries they use to test if batteries fit, with the negative connector being spring loaded they should have made the battery area a couple of mm’s taller to take the taller batteries.