Modern batteries store a very large amount of energy, when fully charged, and need to be treated with respect!
I remember that once, many years ago, I put one of those PP3-type batteries (the ones with press-stud contacts at one end) in my pocket. There were also some coins in my pocket and they made a connection between the contacts. I suddenly realised my jacket was hot and managed to flick the battery out onto the floor – it was almost too hot to touch!
Most modern camera batteries have recessed contacts, which makes this sort of accident less likely, but I always keep spare batteries in self sealing plastic bags or, preferably, in a rigid plastic case
Thank you so much,Mike for helping us all with that valuable information.It’s something that had never crossed my mind.
How my heart sings 
Most of the concerns relate to the batteries.
Modern batteries store a very large amount of energy, when fully charged, and need to be treated with respect!
I remember that once, many years ago, I put one of those PP3-type batteries (the ones with press-stud contacts at one end) in my pocket. There were also some coins in my pocket and they made a connection between the contacts. I suddenly realised my jacket was hot and managed to flick the battery out onto the floor – it was almost too hot to touch!
Most modern camera batteries have recessed contacts, which makes this sort of accident less likely, but I always keep spare batteries in self sealing plastic bags or, preferably, in a rigid plastic case
Thank you so much,Mike for helping us all with that valuable information.It’s something that had never crossed my mind.